Stacked Dynamic Steady-State Flow and Chemistry Profiling for Long-Screened Test Wells Used in Mud Rotary Pilot Holes

This application is a continuation of co-pending U.S. patent application Ser. No. 17/875,178, filed on Jul. 27, 2022, and entitled “STACKED DYNAMIC STEADY-STATE FLOW AND CHEMISTRY PROFILING FOR LONG-SCREENED TEST WELLS USED IN MUD ROTARY PILOT HOLES”. U.S. patent application Ser. No. 17/875,178, claims priority on U.S. Provisional Application Ser. No. 63/247,042, filed on Sep. 22, 2021, and entitled “STACKED DYNAMIC STEADY-STATE FLOW AND CHEMISTRY PROFILING FOR LONG-SCREENED TEST WELLS USED IN MUD ROTARY PILOT HOLES”. As far as permitted, the contents of U.S. patent application Ser. No. 17/875,178, and U.S. Provisional Application Ser. No. 63/247,042, are incorporated herein by reference.

Downhole, vertical delineation of water quality in existing groundwater production and monitoring wells as well as exploratory pilot holes (also sometimes referred to as “boreholes” or “test holes”) is typically financially constrained when acquiring data to locate new public supply wells. As such, wellhead sample concentrations from nearby production wells are used as a make-do approach to identify potential locations for pilot holes that are then used to locate or convert into groundwater production wells. Although use of vertical chemistry and geology is a routine practice in oil and gas exploration when adding more wells to existing oil fields, the groundwater resource market has been slow to adopt the benefits of this standard practice, thus leading to large overruns in construction costs due to failed water chemistry from new wells. Exacerbating this problem is the sparing use of “zone tests”, the temporary test well procedure commonly employed within the pilot hole to delineate vertical distribution of groundwater availability and quality at the location selected or within proximity of the new production well.

The absence of vertical chemistry data from vicinity wells and the spartan approach to vertical testing in the pilot hole sets up a series of cascading data deficiencies where poor water quality at lithologic boundaries exposes the well owner and consultant to risk of cost overruns due to follow-on treatment and blending. Now, there is a real possibility that poor water quality from one or more clay bed boundaries is combined with good water quality from the central portion of permeable zones, thus blending aquifer chemistry to exceed the maximum concentration limits set by government agencies.

is a simplified schematic illustration of a prior art groundwater profiling systemP usable to delineate vertical distribution of groundwater availability and quality at a location selected or within proximity of a new production well. The prior art groundwater profiling systemP is configured to determine groundwater availability and quality by evaluating a plurality of zone test intervals within a given well.

More particularly, as shown in, within the prior art groundwater profiling systemP, a pilot holeP was drilled through one or more aquifersP within a subsurface regionP (below surfaceP) including one or more good, permeable zonesP (three are shown in), as well as one or more clay boundariesP (two are shown in) that separate the permeable zonesP. Additionally, as shown, a prior art test wellP was installed within the pilot holeP, the prior art test wellP including a support casingP and a well screenP. The prior art groundwater profiling systemP further includes a pumpP that is movably positionable within the prior art test wellP. GroundwaterP is illustrated as a means to define the good, permeable zonesP.

As shown, the pilot holeP was drilled for purposes of installing the prior art test wellP. The pilot holeP can be drilled and/or formed in any suitable manner. For example, in the southwestern US, Texas and other states, conventional zone tests are performed in both direct mud rotary and reverse mud rotary pilot holes. Direct mud rotary pilot holes are typically smaller in diameter than reverse mud rotary pilot holes and are typically approximately 12-inches to 14-inches in diameter. Within these holes, 6-inch to 8-inch diameter test wells, respectively, are constructed with varying lengths of well screen, depending on the application. Direct mud rotary wells are either converted into some type of production well, an environmental monitoring well or abandoned. Reverse mud rotary pilot holes are commonly larger than direct rotary pilot holes, oftentimes 14-inches or greater in diameter and are most typically a precursor to production well construction; where the hole is reamed (drilled)-out or enlarged to a diameter in which the production well is constructed. The rationale behind this approach is that the drilling rig used for the large diameter pilot hole is the same rig used for making the hole bigger to construct the new production well, and thereby avoids the need and cost to mobilize a larger, more powerful rig for constructing the production well from a smaller diameter pilot hole. Selection of each zone test interval is based on a review of the drill-cuttings collected during advancement of the pilot hole and from the electric log suite obtained after completion of the pilot hole.

For the test wellP, the support casingP can be a hollow, generally cylinder-shaped structure that extends in a generally downward direction into the subsurface regionP to help provide access to the groundwaterP, and/or other fluids and materials present within the subsurface regionP. The well screenP extends from and/or forms a portion of the support casingP within the subsurface regionP. The well screenP can comprise a perforated pipe that provides an access means through which the groundwaterP enters the test wellP. As illustrated, the well screenP can be adapted to be positioned at a level within the subsurface regionP in vertical alignment with and/or substantially adjacent to the permeable zonesP of the aquiferP to provide ready access to the groundwaterP within the subsurface regionP. Additionally, the well screenP is often provided in a number of individual screened sections that are configured to be positioned only in vertical alignment with and/or substantially adjacent to certain portions of the permeable zonesP.

As shown,illustrates the prior art test wellP being utilized for a Standard Backfill Zone Test in order to delineate vertical distribution of groundwater availability and quality at a location selected or within proximity of a new production well. More specifically,illustrates the prior art groundwater profiling systemP being used to profile the groundwaterP at three different depths within the prior art test wellP. Stated in another manner, the prior art groundwater profiling systemP is shown being used to evaluate groundwater availability and quality within three different zone test intervals, each zone test interval being in vertical alignment with and/or substantially adjacent to one of the permeable zonesP. As shown, the drawing on the left shows use of a first zone test interval in vertical alignment with and/or substantially adjacent to the bottom-most permeable zoneP; the drawing in the center shows use of a second zone test interval in vertical alignment with and/or substantially adjacent to the middle permeable zoneP; and the drawing on the right shows use of a third zone test interval in vertical alignment with and/or substantially adjacent to the upper-most permeable zoneP.

In application within either type of pilot holeP, each conventional zone test is typically constructed with a temporary well screenP that is 10 to 40 feet in length and composed of slotted steel or PVC which is sometimes referred to as a “stove pipe” or “temp well”. A gravel pack envelopeP is installed around the outside of the test wellP and a thin bentonite sealP is emplaced on top of the gravel packP. The test wellP is then developed with the pumpP, e.g., an electric submersible pump, until a low nephelometric unit (NTU) value is reached, which is a quantification of the clarity of the groundwaterP and an indication when most of the drilling fluid has been removed from the zone test interval being tested. Once the test has been completed, the test wellP is then removed from the pilot holeP and the tested interval backfilled with bentonite, ascending the pilot holeP to the next zone test interval. Thus, this process is sometimes referenced as the “Backfill Zone Test” procedure.

The repetitive construction and deconstruction process downhole makes the zone test expensive, labor-intensive, and time-consuming and, as such, limits the number of water quality tests that can be performed, thus leaving large data gaps throughout the saturated length of the pilot hole. More particularly, the cost-basis for the conventional “Backfill Zone Test” procedure typically constrains the number of tests to only 2 to 6 per pilot hole over hundreds of feet of saturated section when using direct and reverse mud rotary, as well as other drilling methods. This data paucity is then complicated by the fact that the temporary well screens are typically only 10 to 40 feet long and are typically placed within the middle of the permeable zonesP, and not near the clay boundariesP where water quality is commonly poor (containing metals, semimetals, radionuclides, etc.).

Thus, unless the pilot hole site is in an area where proven reserves of clean groundwater are available, there is a risk that the well will produce non-compliant groundwater that prevents the well from being used until treatment is installed. Even in areas where the water quality is thought to be good, on a recurring basis, unexpected problems do arise within relatively short distances from other well locations where the water quality is compliant.

Moreover, with existing systems such as shown in, the prior art groundwater profiling systemP often provides results that are not truly reflective of the actual conditions of the groundwaterP within the test wellP. For example, seemingly promising results from the “coarsified” sampling approach, where the focus is on the central areas of the permeable zonesP, may unknowingly provide erroneous confidence that the well will be compliant. Stated in another manner, due to the testing only occurring at or near the middle of intervals of good, clean water, such as within the permeable zonesP, the zone test results may show contaminant concentration levels, such as for arsenic, that are below levels of concern, but which may miss one or more non-compliant zones that may exist within the test wellP. Once receiving such seemingly promising results, a production well is then constructed with screened intervals that intersect the clay beds above and below the permeable zones and sometimes run through the aquitard itself to save money on construction costs. When the new production well is turned-on, the blended concentrations can cause the production well to fail. The essential question to ask now, from a pragmatic standpoint, is if two to six downhole zone-test samples, from the central areas of permeable zones are sufficient to reliably canvass enough vertical distribution to be confident that the final well will be chemically compliant? Based on experience with profiling many hundreds of new wells the answer is “no” since three to four out of every ten new wells appear to fail based on water quality regulations shortly after startup. These wells are then deemed “stranded assets” until the water chemistry issues can be resolved. The new problem initiates a time sink and funding allocation dilemma that leads to overruns of the intended budget since treatment, blending or well modification to block out poor water quality is required to fix the problem.

In summary, the reasons for water quality failure of new wells are varied, but generally, the problems often stem from a lack of subsurface data combined with geologic heterogeneities that are not accounted for near lithologic boundaries that are shared with clay beds. It is at these boundaries where supply wells commonly draw upon poorer water quality from nearby clay zones that contain elevated concentrations of metals, semimetals, radionuclides and other constituents that are blended with better water quality from more central areas of the screen; often resulting in a composite blend concentration at the wellhead that exceeds regulatory limits. When it comes to anthropogenic contaminants, numerous studies have shown that these chemical compounds can “pool” or concentrate on top of clay boundaries as well as be adsorbed onto organic matter embedded within the clay matrix itself; the “electrochemical stickiness” of which can be expressed as a retardation coefficient. When permeable sediments in direct contact with these boundaries are pumped-on, contaminants can be released from these clay beds by different processes including oxidation and change in redox potential, change in pH, desorption, and advective-stripping. Moreover, there is increasing evidence that microbial activity plays a role in the release of certain metals, semi-metals and other compounds at the clay boundaries as well.

Accordingly, it is desired to develop a system and method to inhibit such issues from adversely impacting the ability to locate and develop new public supply wells.

The present invention is directed toward a method for determining dynamic steady-state flow and chemistry of groundwater within a long-screened test well, the method including the steps of (i) drilling a pilot hole through one or more aquifers; (ii) installing a test well within the pilot hole, the test well including a well screen that is at least 40 feet in length; (iii) positioning a pump within the test well, the pump being configured to move the groundwater within the test well; (iv) positioning a packer assembly within the test well, the packer assembly being configured to selectively provide a seal between the test well and the pilot hole; and (v) performing downhole testing at a plurality of different depths within the test well with miniaturized technologies that are equal to or less than 1.5 inches in diameter, the downhole testing being utilized to determine a dynamic steady-state flow and chemistry profile of the groundwater within the test well.

In some embodiments, the pump is an electric submersible pump.

In certain embodiments, the pump and the packer assembly are conjoined together, with the packer assembly including an inflatable packer that is attached to the pump near a bottom of the pump.

In various embodiments, the pump is used at a first depth within the test well and then is moved from the first depth to a second depth within the test well that is different than the first depth to perform stacked dynamic steady-state flow and chemistry profiles.

In some embodiments, the step of drilling includes evaluating cuttings and core removed during drilling of the pilot hole for at least one of type of rock, type of sediment and water bearing properties.

In certain embodiments, drill cuttings and electric logs are used to locate screened intervals of the well screen and to develop a tracer injection and sampling plan to be implemented with the miniaturized technologies.

In alternative embodiments, the step of drilling includes drilling the pilot hole using one of (i) a direct mud rotary drilling method that is configured to drill the pilot hole having a diameter of between approximately 12 inches and 14 inches; and (ii) a reverse mud rotary drilling method that is configured to drill the pilot hole having a diameter of at least approximately 14 inches.

In many embodiments, the miniaturized technologies include a tracer injection system that is configured to determine downhole velocity and flow measurements of the groundwater within the test well.

In some embodiments, the tracer injection system includes a flexible tube that is filled with a tracer material, the flexible tube being configured to inject the tracer material sideways into the groundwater within the test well to determine the downhole velocity and flow measurements. Air bubbles are inhibited from entering the flexible tube. Timing of injection of the tracer material from the flexible tube into the groundwater within the test well can be controlled at least in part by a timer control unit.

In certain embodiments, the miniaturized technologies further include a groundwater sampling system that is configured to selectively remove groundwater samples from the test well.

In some embodiments, the tracer injection system and the groundwater sampling system are joined into a single, conjoined, downhole unit so that the tracer injection system and the groundwater sampling system move together to different depths within the test well.

In various embodiments, the miniaturized technologies include a groundwater sampling system that is configured to selectively remove groundwater samples from the test well.

In certain embodiments, the groundwater sampling system includes a miniaturized pump, a section of jacketed tubing, and a volume booster. The section of jacketed tubing can include a first tube that is configured to deliver compressed gas from a surface level to a targeted sampling depth, and a second tube that is configured to transfer groundwater from the targeted sampling depth to the surface level.

In some applications, the present invention is further directed toward a flow and chemistry profiling system for determining dynamic steady-state flow and chemistry of groundwater within a long-screened test well, the flow and chemistry profiling system including (i) a pilot hole that is drilled through one or more aquifers; (ii) a test well that is installed within the pilot hole, the test well including a well screen that is at least 40 feet in length; (iii) a pump that is positioned within the test well, the pump being configured to move the groundwater within the test well; (iv) a packer assembly that is positioned within the test well, the packer assembly being configured to selectively provide a seal between the test well and the pilot hole; and (v) miniaturized technologies that are utilized for performing downhole testing at a plurality of different depths within the test well, the miniaturized technologies being equal to or less than 1.5 inches in diameter, the downhole testing being utilized to determine a dynamic steady-state flow and chemistry profile of the groundwater within the test well.

Embodiments of the present invention are described herein in the context of a system and method for overcoming and/or minimizing potential issues impacting the ability to locate and develop new public supply wells by using a new vertical exploration method and technological advancement called “Stacked Dynamic Flow and Chemistry Profiling (SDP) in Long Screened Test Wells”. Accomplished with miniaturized profiling technologies, the entire profiling system costs from slightly less to modestly more than conventional zone testing. SDP multiplies vertical delineation of water chemistry downhole by four to eight times and can be performed in significantly less time than traditional zone tests. SDP can also provide a more technically robust and conservative approach to identifying water quality risks prior to well construction.

The SDP approach is particularly useful when weighing the cost of treatment and/or blending system construction as well as long-term operation and maintenance if the new well should happen to fail because it did not meet water quality regulations. When this problem arises, the true cost of the well is the total cost of the well plus the treatment(s) or blending system(s) required to bring its water supply on-line. A failed well can be a tough economic and political pill to swallow since utilities and rate payers alike end up shouldering the increasing costs over time that are needed to build and operate these facilities. Moreover, some of the treatment technologies are complex and difficult to operate. Finding qualified operators and being able to sustainably cover their labor costs year over year is potentially a challenge unto itself. High resolution, rapid pilot hole characterization using SDP can limit both short-term and long-term risks from the ever-present potential of new well water quality problems.

Even though the process might be equal to or even a little bit more expensive than traditional zone testing, it can function as a robust insurance policy to reduce risk from the stated consequences. The long-screened test well provides the opportunity to rapidly test many more locations that are potentially geochemically problematic rather than an exclusive focus on the mid-section of the permeable zones based on affordability and where the water quality is often the best. This data can then be used to better inform the construction process of the well screens in terms of their vertical length and how much buffer distance should be allocated between the well screen and adjoining clay beds.

Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same or similar reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.

In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application-related and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

The description of the invention below provides the basic set up, detailed operating components and procedures, and flow and mass balance calculations for using stacked dynamic profiling (SDP) in temporary long-screened test wells in lieu of traditional, temporary short-screened zone tests.

is a simplified flowchart illustrating general operational procedures of a system and method for determining dynamic steady-state flow and chemistry of groundwater within a long-screened test well. It is appreciated that, in certain applications, the steps delineated herein can be modified, reordered, combined, or omitted, and additional steps can be added without deviating from the intended breadth and scope of the present invention.

At step, a pilot hole is drilled through one or more aquifers. In various embodiments, the pilot hole (also sometimes referred to as a “test hole” or “borehole”) is drilled through the one or more aquifers for the purpose of building a test well and subsequently a groundwater supply well. In certain non-exclusive implementations, the aquifers can be located in sedimentary basins and in fractured bedrock, and can be of any depth.

At step, a test well is installed within the pilot hole.

Referring now to,is a simplified schematic illustration showing use of a pumpto develop a test wellwithin a pilot holeas part of a groundwater flow and chemistry profiling system(also sometimes referred to herein as a “groundwater profiling system” or simply a “profiling system”) by drilling fluid leaked into the surrounding formation during the drilling process. Additionally,is a simplified schematic illustration showing construction of the long-screened test wellwithin the pilot holefor the groundwater profiling system.

As shown, the pilot holehas been drilled into one or more aquiferswithin a subsurface region(below surface) including one or more good, permeable zones, as well as one or more clay boundariesthat separate the permeable zones.

The pilot holecan be drilled and/or formed in any suitable manner. For example, the pilot holecan be drilled with any method, including mud and air rotary, reverse rotary, sonic, dual-tube percussion, dual-tube rotary, air rotary casing hammer, cable tool, auger, direct push, or any other suitable method. The pilot holecan also be of any diameter, the purpose of which is to build a long-screened test wellin advance of the groundwater supply well for the purpose of profiling for zonal flow and chemistry. In one non-exclusive implementation, the pilot holecan be a small diameter pilot hole, such as between approximately 12 inches and 14 inches in diameter, that can be drilled using a direct mud rotary drilling method. In another non-exclusive implementation, the pilot holecan be a large diameter pilot hole, such as larger than approximately 14 inches or larger than approximately 17.5 inches in diameter, that can be drilled using a reverse mud rotary drilling method.

In some cases, within bedrock or other hard rock environments, where the rock materials are competent, and will not collapse into the pilot hole, the bedrock itself can comprise the test well, without having to construct a separate test well to support the pilot holeto inhibit it from collapsing.

As the pilot holeis being drilled to total depth, the cuttings and core removed from the pilot holeare evaluated and catalogued to evaluate the sediment or rock types and their water bearing properties including grain size distribution and type, as well as rock types and fracture bearing qualities. After the total depth of the pilot holeis reached, an optional step is to run downhole geophysical equipment such as resistivity, spontaneous potential, gamma ray, neutron, density, induction or any other type of probe or sensor to generate data that can be used to infer the sediment type, rock type and basic formational parameters such as permeability, porosity, saturation, salinity, conductivity and others. In bedrock pilot holes, even downhole video cameras can be used to identify the depth and characteristics of rock fractures and lineaments that intersect the pilot hole.

In cases where the pilot holecould collapse, the collective data is then used to design the test well, which can be made from any number of materials including any type of steel, PVC, carbon fiber, fiberglass and so on. The decision on which material to use for construction of the test welldepends at least in part on the depth of the pilot hole. For smaller diameter pilot holes, such as in the 12-inch to 14-inch range, the preferred diameter of the test wellis 6 inches to 8 inches, respectively, to achieve pumping rates ranging between 100 to 300 GPM. Larger diameter pilot holesallow for larger diameter test wellswhere higher pumping rates can be achieved.

As illustrated, the test wellcan include a support casingand a well screen. For the test well, the support casingcan be a hollow, generally cylinder-shaped structure that extends in a generally downward direction into the subsurface regionto help provide access to groundwater, and/or other fluids and materials present within the subsurface region. The well screenextends from and/or forms a portion of the support casingwithin the subsurface region. The well screencan comprise a perforated pipe that provides an access means through which the groundwaterenters the test well. In certain embodiments, the test wellcan have more than 40 feet of well screen, and quite often can haveto many hundreds of feet of well screen, either continuous or in sections, and being of any suitable diameter.

In alternative embodiments, the test wellis typically constructed with either a continuous gravel pack envelope(as illustrated more clearly, for example, in) around the outside of the test welland located between the test welland the formation wall of the pilot hole, or installed in layers where it alternates with seals(as illustrated more clearly, for example, in), such as bentonite seals and/or cement seals, that are aligned with fine-grained units such as clays and silts or even fine-grained rock types lacking fractures through which groundwatercan flow. In some embodiments, the gravel packis installed in sections of varying lengths with the sealsin between, the purpose of the sealsbeing to inhibit vertical migration of naturally occurring or anthropogenic contaminants through the gravel packfrom one or more water bearing units to one or more receiving water bearing units, before, during or after testing.

The test wellmay also have a sanitary seal (not shown) between the top (or shallowest depth) of the gravel packand the ground surface, such seal being installed to inhibit migration of contaminants from the ground surfacevertically downward along the outside of the test well. Such seal can be composed of any type of cement or bentonite mixture.

Following completion of initial test wellconstruction, the test wellis developed, meaning that the drill flour, drilling fluid and mud cake, drilling fluid dispersants and other residual materials that have adhered to the pilot hole wall and/or have invaded into the surrounding formation are removed from the pilot holeusing various methods including a swab, surge block, pump, and air lifting, as well as other methods, until the groundwateris satisfactorily clear for testing and sampling. Such a process is illustrated invia series of concentric ovals.

In either case, the pumpcan be an electric submersible pump that is usable in the development and as part of the groundwater sampling process that follows.

It is recognized that the support casingor well screenmay not be precisely vertical at all locations throughout the test well. In fact, the support casingor well screenmay be off-vertical by several degrees (or more) at certain locations along the depth of the test well. However, it is the intent of the groundwater profiling systemthat certain components be utilized substantially perpendicularly to a longitudinal axisX of the support casingand/or well screenof the test well.

Returning to, at step, a pump is positioned within the test well, the pump being configured to move groundwater within the test well.