Assessment of Environmental Implications of Abandoned Oil and Gas Wells
- D.L. Warner (U. of Missouri-Rolla) | C.L. McConnell (U. of Missouri-Rolla)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- September 1993
- Document Type
- Journal Paper
- 874 - 880
- 1993. Society of Petroleum Engineers
- 4.3.4 Scale, 2.4.3 Sand/Solids Control, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 6.5.2 Water use, produced water discharge and disposal, 1.11 Drilling Fluids and Materials, 4.3.1 Hydrates, 5.2 Reservoir Fluid Dynamics, 1.14 Casing and Cementing, 4.2.3 Materials and Corrosion, 1.6.11 Plugging and Abandonment, 4.1.5 Processing Equipment, 2.2.2 Perforating, 6.5.3 Waste Management, 1.10 Drilling Equipment
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A detailed study was made of the potential for abandoned oil and gas wellsin the Lower Tuscaloosa sand of Mississippi and Louisiana to act as conduitsfor movement of saline water from the Lower Tuscaloosa into underground sourcesof drinking water (USDW's). Finite-difference numerical modeling determined theextent that water might be forced from the Lower Tuscaloosa sand into a USDW asa result of injection into the Lower Tuscaloosa. Within the range of conditionsmodeled, water from the Lower Tuscaloosa never traveled into a USDW. On thebasis of the modeling, we concluded that it is unlikely that abandoned oil andgas wells in the Lower Tuscaloosa would serve as conduits for water movementfrom the trend into a USDW. The procedures developed in this study should bereadily applicable to analysis of the potential for abandoned wells to act aspathways for contaminant flow into USDW's in other oil and gas producing areasof the country.
Purpose and Scope of Study. Because of the increasing focus by Purpose andScope of Study. Because of the increasing focus by U.S. regulatory agencies onabandoned oil and gas wells, the U. of Missouri-Rolla conducted research toassess the potential for abandoned oil and gas wells in the Lower Tuscaloosasand oil-producing trend of Mississippi and Louisiana to act as conduits forflow of saline water from the Lower Tuscaloosa into USDW's. Fig. 1 showslocations of selected wells from oil fields in the Lower Tuscaloosa sand. TheLower Tuscaloosa sand trend extends for about 135 miles from south-centralMississippi northwest into eastern Louisiana and for about 100 miles from northto south. The study included assembly of geologic and engineering data toformulate numerical models to simulate the range of flow conditions throughabandoned wells in the Lower Tuscaloosa trend. The final step in the study wasthe actual numerical simulation of flow conditions for these abandoned wells.The simulations performed are believed to represent conditions throughout theLower Tuscaloosa sand and the conclusions should be applicable to all abandonedLower Tuscaloosa sand wells. The study is intended as an example that can bereplicated in other oil- and gas-producing areas with similar conditions. Toconduct such a study, sufficient information concerning the subsurface geologyand hydrology, oil production history, and historic well construction andabandonment practices must exist or be possible to obtain to develop arealistic computer model. Also, geologic and hydrologic conditions that aresufficiently consistent over some area or distance are needed for the model tobe represent enough cases to make modeling worthwhile. One would not be likelyto conduct such modeling where every injection well required formulation of anew model.
Previous Work. Ward et al. 2 performed the first numerical Previous Work.Ward et al. 2 performed the first numerical modeling work on the movement offluids through an abandoned well. Ward et al. modeled the leakage of injectedcontaminants through an abandoned unplugged borehole. The work demonstrated thecapability of the SWIFT III model for such investigations, but has no directapplication to the problem studied here. Ward et al.'s investigation involvedtracking wastes moving from an injection well to and up through an abandonedwell. The problem here involves tracking the movement of native saline waterfrom a saline-water-bearing aquifer in response to the pressure created by aninjection well. Although significant difference exist in the details of the twoproblems, most procedures in setting up the models and data input are the same.In the modeling of injected waste movement, the injected fluid was tagged andtracked and no attention was given to the native saline water residing in theinjection reservoir. In this problem, the injection fluid was assumed to thesame as the native saline water and all the water that moved up the boreholewas considered a potential contaminant to USDW. Warner modeled the response ofa specific existing abandoned well in the West Mallalieu oil field to injectionthrough a nearby water-injection well. Javendel et al. developed an analyticalmodel of the abandoned well problem. While this model cannot be used todetermine the effect of an abandoned well on the quality of groundwater in aUSDW, it allows calculation of the gross amount of water that can flow into anabandoned well and thus provides a means to compare the results of numericalmodeling of the flow into an abandoned well with a much simpler analyticalcalculation. The Javendel analytical model was used to verify the accuracy offlow results obtained from the numerical model during calibration.
Abandoned Well Problem
Thousands of wells have been drilled and abandoned during the 130-yearhistory of the U.S. petroleum industry. Regulations for plugging these wells,nonexistent in the early days of the plugging these wells, nonexistent in theearly days of the industry, have evolved over the years to their presenteffective level. Thus, an unknown but large number of abandoned wells existthat may be unplugged or inadequately plugged by today's standards. As a resultof incidents in which abandoned wells were implicated as sources of groundwatercontamination, such wells are often considered indiscriminately to be potentialpathways for contamination of a USDW. Contamination can result frominteraquifer flow of natural formation water or by transmission of injectedfluids from the injection reservoir to a USDW.
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