Development of Improved Oil Field Waste Injection Disposal Techniques

This Final Report summarizes Terralog's efforts and results for the project "Development of Improved Fracture Injection Disposal Techniques for Oilfield Waste", completed under DOE Contract DE-AC26-99BCI5222. The goals of this project have been to: 1) assemble and analyze a comprehensive database of past waste injection operations; 2) develop improved diagnostic techniques for monitoring fracture growth and formation changes; 3) develop operating guidelines to optimize daily operations and ultimate storage capacity of the target formation; and 4) to apply these improved models and guidelines in the field. Terralog Technologies first assembled a Slurry Fracture Injection (SFI) database template, and populated it with the monitoring data collected from eight oil field waste injection projects, comprising a total of more than 700 injection episodes. Pressure and rate data was analyzed using fracture models and well test analysis to determine the characteristics of fractures, the permeability of the surrounding formation, and the changing in-situ stress conditions. The database is created in Microsoft ACCESS format. Terralog also created two plotting programs within Access in order to graphically view the data for visual interpretation. The power of the SFI database is that different variables can be plotted easily using the Microsoft Access program. Data from different projects can be compared directly. Cross plots of various injection parameters and observations can be made, with filtering on a third variable. The database and query tools were applied to investigate a number of correlations between operating parameters and formation response, providing insight and useful information for optimizing future injection operations. Terralog next investigated the use of two dimensional analytical models (Perkins-KernNordgren) and pseudo three-dimensional models (FRACPRO) to simulate slurry fracture injection. These were modified to allow variations in shear modulus, leakoff coefficients, and closure stress with repeated injection episodes in order to capture observed formation behavior. Varying these parameters provides improvement over typical constant value assumptions. Terralog also investigated the use of coupled fluid flow and particle flow models to simulate fracture and dilation processes during waste injection. These studies lead us to conclude that when formations are weakly cemented with limited shear strength, there is a transition from brittle, discrete fracture extension, to more wide scale dilation and inelastic parting. We successfully developed a coupling process between a continuum flow model and a discrete particle model, allowing simulation of slurry particle injection and resulting fracture and dilation. The method shows good potential for better simulating waste injection, and warrants additional investigation and development effort. Using insights and observations from the database analysis and modeling efforts, Terralog next developed design and operating guidelines for fracture injection projects. Some of these recommendations were incorporated into new fracture injection regulations established by the Louisiana Department of Natural Resources, and approved by the US EPA. Some recommendations have also been informally accepted as "best-practices" in the State of California by the California Division of Oil and Gas. Terralog applied these guidelines to design and submit permit applications for three new injection projects in California. Finally, Terralog applied some of the modeling techniques developed through this project to a Slurry Fracture Injection project in Long Beach, California. In February, 2002, Terralog collaborated with THUMS Long Beach Company to review and analyze waste injection into a new interval of the Lower Terminal formation in the Wilmington Oilfield. We evaluated operations over a two-week period from February 18 to February 29,2002, during which about 6000 bbls of waste slurry was injected, and successfully model injection behavior by taking into account changing formation properties.

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