Brine Disposal Into a Tight Stress-Sensitive Formation at Fracturing Conditions: Design and Field Experience
- Antonin Settari (Duke Engineering & Services Inc.) | G.M. Warren (Duke Engineering & Services Inc.) | Jerome Jacquemont (Sofregaz U.S. Inc.) | Paul Bieniawski (Sofregaz U.S. Inc.) | Michel Dussaud (Sofregaz U.S. Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- April 1999
- Document Type
- Journal Paper
- 186 - 195
- 1999. Society of Petroleum Engineers
- 5.1.5 Geologic Modeling, 4.1.2 Separation and Treating, 6.5.3 Waste Management, 4.6 Natural Gas, 5.1 Reservoir Characterisation, 4.2 Pipelines, Flowlines and Risers, 5.5.2 Core Analysis, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.6.4 Drillstem/Well Testing, 3 Production and Well Operations, 1.14 Casing and Cementing, 2.2.2 Perforating, 1.2.2 Geomechanics, 5.1.2 Faults and Fracture Characterisation, 5.8.6 Naturally Fractured Reservoir, 1.6 Drilling Operations, 5.8.7 Carbonate Reservoir, 1.2.3 Rock properties, 5.5.8 History Matching, 5.4.1 Waterflooding, 2.4.3 Sand/Solids Control, 5.3.4 Integration of geomechanics in models, 5.8.5 Oil Sand, Oil Shale, Bitumen, 4.1.5 Processing Equipment, 5.5 Reservoir Simulation
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This paper describes a study of the potential of a tight reservoir zone for disposal of brine generated in salt cavern leaching operations. The study included field injection testing, numerical analysis using uncoupled and coupled reservoir, geomechanical and fracturing modeling, laboratory work and design of a field injection monitoring program. It was shown that a surprising brine disposal capacity exists in the tight (0.03 md) Oriskany target formation. Initial screening was followed by carefully designed injection testing, laboratory work and subsequent evaluation with the aid of detailed coupled fracture and reservoir numerical models, and numerical well test analysis. Low initial estimates of brine disposal capacity were increased significantly by incorporating more sophisticated, coupled reservoir and geomechanical numerical models. The models, which account for stress dependent porosity and permeability and fracture propagation, were calibrated to laboratory and field test data. Using these models, an excellent match of the injection data was obtained, and predictions of injectivity were made under various project scenarios. The coupled model has been also used to design the monitoring program for the first phase of the injection operations.
Gas storage in salt caverns has many advantages over conventional storage operations in reservoirs. In the U.S. alone, over 30 caverns have been built and put into operation. On the other hand, the selection of the site, design and execution of the leaching process, commissioning, operating and monitoring the caverns requires specialized, multidisciplinary technology.1,2 This paper deals only with one facet of the overall process, namely, the disposal of the brine generated during the leaching process by reinjection. This topic has many similarities to other injection processes in petroleum engineering and will be of interest to those working in waterflooding or waste disposal at or near fracturing conditions, and in geomechanics and fracturing.
In cavern leaching operations, large amounts of concentrated brine are generated which need to be treated or disposed of. In general, there are several ways to dispose of or utilize the brine, such as selling it for salt products manufacture, building a salt product manufacturing plant, disposal in suitable permeable formations, or even pipelining to the sea. The economical and environmental aspects of each alternative guide the selection of the best method (or combination of several methods). Even more importantly, the efficiency of the brine disposal is one of the critical elements for the economics of a planned cavern gas storage project. In the subject project described below, disposal by reinjecting the brine was considered in conjunction with selling the majority of the brine to a salt product company.
The Tioga Gas Storage Project
The location of the project in Tioga, Pennsylvania, was selected by its developer Market Hub Partners (MHP) based on gas market analysis and geological considerations. Key elements included finding a salt formation which would be an excellent candidate for cavern leaching, close to existing pipelines and infrastructure. Such a formation was found below the existing Tioga gas storage field. As shown in Fig. 1, MHP is planning to build up to ten storage caverns in this massive (2200 ft thick) salt formation, separated from the Oriskany gas storage formation by 400 ft of limestone and anhydrite shale. The structural crossection of the storage site, with a proposed cavern location, is shown in Fig. 2. Each cavern will provide around 2,500,000 MScf of storage and in the process of leaching will generate about 25 million bbls of brine per cavern. These fluid volumes provide a large incentive to find a suitable horizon for disposal of the brine, and to prove up the injection capacity.
Disposal Site Selection and Geology
Two sites were selected for brine disposal, based on a geological review including the interpretation of 7 seismic lines and 120 wells in the vicinity of the Tioga storage pool.
The brine disposal areas are 1.5 miles south of the gas storage field, and isolated from it by a series of faults of more than 1,000 ft of thrust (see Fig. 2). The target injection zone consists of the middle Devonian Oriskany sandstone and Helderberg limestone. These formations are isolated from the shallow drinking water aquifer by 4,800 ft of upper Devonian shales, including a strike of very tight limestone. The underlying formations consist of a layer of anhydrite on top of the salt section (Salina). The first brine disposal test well SWD#01 (see Fig. 3) was drilled in June 1995 and confirmed the results of the geological review. SWD#01 was cored in the Oriskany, Helderberg, Anhydrite and salt.
Exploratory Testing of the Target Zones
A first DST, followed by the injection of 600 barrels of brine, was performed in the Oriskany. The injection/fall-off test was conducted above parting pressure, in order to achieve a commercial rate (22 gpm). The well was then deepened to reach TD, at 5,750 ft GL. A set of logs were run, including an FMI log, which confirmed an induced fracture in the Oriskany zone.
A second DST was performed, in the Oriskany, Helderberg, and Anhydrite sections, followed by the injection of 1,200 barrels of brine. The pressure signature was similar to DST#1. A second FMI log was conducted, which exhibited new induced fracturing in the Helderberg. SWD#01 was then cased, cemented and perforated in the Oriskany and Helderberg. Stress tests were conducted in the Oriskany and the Helderberg.
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