Salt Water Disposal (SWD) Wells: Advances in Evaluating their Environmental Impact

Transcription

1 Salt Water Disposal (SWD) Wells: Advances in Evaluating their Environmental Impact Texas Alliance of Groundwater Districts Summit San Marcos, Texas August 26, 2015 Ronald T. Green, Ph.D., P.G., F. Paul Bertetti, P.G., and Nate Toll Geosciences and Engineering Division Southwest Research Institute

2 Evaluate risks from proposed salt water disposal (SWD) wells: Dramatic increase in SWD activity resulting from highvolume liquid waste and produced water from fracking SWDs are regulated by the Texas Railroad Commission Groundwater Conservation Districts (GCDs) have standing

3 Role of GCDs in SWD Well Activity GCDs do not regulate SWD wells, but do have opportunity to provide input on whether SWD wells can impact groundwater GCDs can provide input on construction of SWDs GCDs can provide input on location of SWDs as it affects groundwater GCDs role in assessing need and other impacts due to location

4 Factors that GCDs Can Evaluate to Mitigate Threat of Contamination due to SWD Wells Evaluate water quality of injection horizon Evaluate secondary containment: Impervious lining Sufficient capacity Evaluate well construction: Surface casing through USDW Protect entire long string with cement Monitor/document SWD: Document cement in well using cement bond log (CBL) Measure and document pressure daily Insure proposed injection pressures will not lead to unintended risks Evaluate for risk of induced seismicity

5 Water Quality of Injection Horizon

6 Water Quality of Injection Horizon Depth of Water Wells Water Quality Designation Water Quality Designation TDS Formation 500 Carrizo < 3,000 ppm BUQW 1,200 Fresh Wilcox Formation? 3,000 ppm- 10,000 ppm USDW 5,000 Brackish Wilcox Formation 15,000 Saline Wilcox Formation 80,000 Confining Unit 110,000 Edwards Formation 3,000 ppm- 10,000 ppm USDW 5,000 Glen Rose Formation

7 Important factors on construction of SWD wells that could impact groundwater Impact of SWDs at the surface Impact of SWDs underground

8 Impact of SWDs at the Surface Secondary Containment

9 What is Secondary Containment? Primary Containment Freshwater aquifer Secondary Containment Confining layer Injection horizon

10 One type of secondary containment

11 Another type of secondary containment

12 Why is Secondary Containment Important?

13 Accidents +

14 Limited Tank Failure

15 Catastrophic Tank Battery Failure

16 Secondary Containment Sufficient Capacity Sufficiently Impervious

17 Secondary Containment (1) Sufficient Capacity Texas RRC: Secondary containment systems must be capable of preventing the migration of accumulated liquid out of the system and capable of detecting and collecting releases until the collected material is removed. Spill Prevention, Control and Countermeasures (SPCC) 40 CFR 112 (EPA) All tank battery, separation and treating installations must have secondary containment for entire capacity of largest single container and sufficient freeboard to contain precipitation. Objective: Insure secondary containment of tank battery has sufficient capacity to retain spilled waste liquids in the event of catastrophic failure. What is Sufficient Capacity? 100% of capacity of all tanks in battery Tank displacement 24-hour, 25-yr rain event V = L W H H L W

18 Secondary Containment (2) Sufficiently Impervious Texas RRC: Secondary containment systems must be capable of preventing the migration of accumulated liquid out of the system and capable of detecting and collecting releases until the collected material is removed. Objective: Insure secondary containment of tank battery is sufficiently impervious to retain spilled waste liquids in the event of spills and leaks.

19 Impact of SWDs Underground SWD Well Construction

20 SWD Well Construction Main components of interest to GCDs: Well head with gauges Surface casing Long string Tubing Cement

21 Key Criteria in SWD Well Construction Injection Well Surface casing should extend through base of Underground Source of Drinking Water (USDW) All of surface casing should be cemented surface casing long string BOQW USDW cement Long string casing goes from surface to bottom of borehole Entire long string should be cemented, at least several 100s ft into surface casing Use DV tool with variable weight cements to cement long string injection horizon Confirm cement behind long string using cement bond log (CBL) Install pressure gauges at well head, measure continuously, record daily

22 Threats from Aged or Improperly Abandoned Wells and Boreholes

23 Key Criteria when Evaluating Abandoned and Plugged Wells and Boreholes Injection Well Date! Older technology may not be adequate BOQW USDW Was base of USDW and BOQW sealed off? Were plugs placed within confining layers? cement Was mud left in borehole? Weight of mud? injection horizon Details on cement?

24 At what distance are neighboring wells a concern?

25 Threat from Abandoned Wells Breakout Unknown threat from hydraulic fracturing by deep-well injection of waste fluids

26 At What Distance are Abandoned Wells a Threat? Disposal Well Permit Regulation (Texas) Predicated on Isotropic Media the applicant shall review wells that penetrate the proposed disposal zone within a 1/4 mile radius of the proposed disposal well to determine if all abandoned wells have been plugged in a manner that will prevent the movement of fluids from the disposal zone into freshwater strata. This regulation assumes radial flow and does not account for heterogeneity that could result from stress-field induced directional flow

27 Homogeneous and Isotropic Injection Plume Geometry and Size Uniform growth of injection plume under homogeneous and isotropic conditions.

28 Stress-field Induced Preferential Flow Injected fluids tend to follow existing fractures consistent with pre-existing stress field instead of an isotropic sphere An injection well has greater influence in the direction of maximum horizontal stress and major faults and fractures

29 Geomechanical Modeling Can Provide Insights on How Fluids Actually Migrate through Rock Horizontal borehole through mechanically stratified system Horizontal beds Horizontal beds plus pre-existing fault Dipping beds 100 m by ~50 m model domain ~1-2 m long perforated interval 60 minutes injection Initial anisotropic stress state s 1 = s v (variable reservoir depths) s 3 = s h parallel to wellbore

30 Geomechanical Modeling Damage due to Compressive/Shear failure Damage due to Tensile Failure Depth 1 km (3,300 ft) Depth 3 km (9,800 ft) Effect of Tilting Beds

31 Although this is closer to reality, this is what is considered by the Railroad Commission

32 Calculating Pressure Buildup from a SWD Well Pressure buildup is calculated using the Theis equation where it is assumed that the injection thickness, permeability, and porosity are constant in all directions p = Qμ kb log kt θμcr

33 Evaluating Threats Posed by Geriatric/Abandoned Wells

34 Example #1: SWD Well Near a Abandoned Well Injection Horizon is Fully-Pressurized Injection at High Pressures is Not Acceptable

35 Existing Dry Borehole 0.2 miles from the Proposed SWD Well Proposed SWD well 0.2 mile Dry Hole Shaded circle has 0.25-mile radius 35

36 Depth Dry Hole Pressure Buildup After 1 Year Expressed in Terms of Head (ft of water) Total head = elevation head + pressure head h t = h e + h p = h e + P/ρg Injection pressure = 1,260 psi = 2,848 ft of water h t = 2,520 +2,848 ft = 5,368 ft Proposed SWD 0 ft 300 ft Cement Carrizo h t = 1, ft = 2,220 ft Fresh Wilcox Formation Saline Wilcox Formation 700 ft 760 ft 1,000 ft 1,236 ft Midway Formation 1,545 ft Navarro Formation 2,520 ft 3,120 ft h t = 0 + (2, ) ft = 2,259 ft Olmos Formation h t = 0 + (2,520 +2,848 ft ) = 5,368 ft 3,373 ft San Miguel Formation 4,224 ft ft

37 Example #2: SWD Well Near a Geriatric Well Field Injection Horizon is Under-Pressurized Injection at Low Pressures is Acceptable

38 38 Proposed Disposal Well Geriatric Well Field (Permian Basin, Texas) Proposed Disposal Well Existing Well

39 Depth Existing Well Pressure Buildup Expressed in Terms of Head (ft of water) Total head = elevation head + pressure head h t = h e + h p = h e + ρgh Injection pressure = 200 psi = 452 ft of water h t = 2, ft = 3,052 ft Proposed SWD 0 ft 300 ft Dockum Formation 600 ft Rustler Formation 1,100 ft Confining Unit 2,240 ft h t = ft = 360 ft Queen Formation 2,400 ft 2,450 ft 2,500 ft Grayburg Formation 2,600 ft h t = 0 + ( ) ft = 360 ft h t = 0 + ( ) ft = 575 ft 2,600 ft 2,605 ft 1,320 ft 39

40 SWD Locations near Old/Existing Wells Is it Acceptable? In this case.no In this case.yes Carrizo Fresh Wilcox Formation Saline Wilcox Formation Midway Formation Navarro Formation Olmos Formation Dockum Formation Rustler Formation Confining Unit Queen Formation Grayburg Formation San Miguel Formation

41 Example of Breakout from Injection Wells (Mogford Well)

42 Surface Breakout from Disposal Well Operating Disposal Well Breakout occurred after 4 years of injection in an abandoned and plugged well located over ¼ mile away

43 Pressure (psig) Recorded Pressures at Sandy SWD (H-10) Time of breakout Start of injection 0 Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 Date 43

44 Total Volume Injected (BBLs/mth) Recorded Injected Volumes at Sandy SWD (H-10) 120, ,000 80,000 60,000 40,000 20,000 0 Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 Date 44

45 Depth Mogford Well Pressure Buildup Expressed in Terms of Head (ft of water) Carrizo Formation Wilcox Formation Total head = elevation head + pressure head h t = h e + h p = h e + ρgh Injection pressure = 1,700 psi = 3,842 ft of water h t = 0+ (3, ft) = 3,472 ft h t = 3, ,842 ft = 7,389 ft Sandy SWD ft 300 ft 600 ft 1,350 ft Head, h e 3,547 ft 3,247 ft 2,947 ft 2,497 ft Midway Formation Escondido Formation 3,196 ft 351 ft Olmos Formation 3,545 ft h t = 0+ (3, ft) = 3,472 ft h t = 0+ (3, ,842 ft) = 7,089 ft 3,547 ft 3,576 ft 0 ft -29 ft 1,747 ft 45

46 Seismic Events Induced by Disposal Wells

47 Number of Events Increase in the Level of Seismicity in Texas Subsequent to Onset of Increased Oil/Gas Activity 475 Texas Cumulative Seismic Events Event /3/1954 6/11/1968 2/18/ /28/1995 7/6/2009 3/15/2023 Event Date Data from Iris event browser downloaded

48 Locations of Potentially Induced Earthquakes (USGS Report 2015) 48 Petersen, et a, 2015, Incorporating induced seismicity in the 2014 United States National Seismic Hazard Model Results of 2014 workshop and sensitivity studies: U.S. Geological Survey Open-File Report , 69 p.,

49 Texas RRC Current Perspective on Induced Earthquakes Mar 28, The Railroad Commission of Texas hired a seismologist, Dr. David Craig Pearson. Motivated by two earthquakes in Barnett Shale (Azle, TX) April 21, Azle study published: the result of a yearlong collaboration among 11 researchers at SMU, the University of Texas at Austin and the U.S. Geological Survey. When you look at the breadth of data available, we would argue that the most obvious cause, the most likely cause, is oil and gas activity, said the study s lead author Matthew Hornbach. June 5, I have not reached the conclusion that oil and gas activity is the causal factor, said Craig Pearson, the Railroad Commission s staff seismologist. While we remain concerned about seismic activity in the state, we still haven t had a hearing where we ve had a definite case made that a specific operator is associated with any specific earthquake activity.

50 Maximum Seismic Moment (i.e., earthquake) Possible Increases with Total Volume of Injected Fluid Risk of inducing an earthquake increases with the total volume of injected waste From: McGarr, A. (2014), Maximum magnitude earthquakes induced by fluid injection, J. Geophys. Res. Solid Earth, 119, , doi: /2013jb

51 Factors that GCDs Can Evaluate to Mitigate Threat of Contamination due to SWD Wells Evaluate water quality of injection horizon Evaluate secondary containment: Impervious lining Sufficient capacity Evaluate well construction: Surface casing through USDW Protect entire long string with cement Monitor/document SWD: Document cement in well using cement bond log (CBL) Measure and document pressure daily Insure proposed injection pressures will not lead to unintended risks Evaluate for risk of induced seismicity

52 Contact Information Ronald T. Green, Ph.D., P.G. Institute Scientist Geosciences and Engineering Division Southwest Research Institute 6220 Culebra San Antonio, Texas (office) (fax) (cell)