Brine Disposal into a Tight Stress Sensitive Formation at Fracturing Conditions: Design and Field Experience
Authors: Settari A. , Warren G.M. , Jacquemont J. , Bieniawski P. , Dussaud M. 
Published: December 2007

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.

Introduction

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. This paper deals only with one facet of the overall process, namely, the disposal of the brine generated during the leaching process by re-injection. 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 re-injecting the brine was considered in conjunction with selling the majority of the brine to a salt product company.

The Tioga gas storage project

The subject Tioga cavern storage project is being developed by Market Hub Partners (MHP) which is a limited partnership owned by TPC Gas Storage Services, L.P.; Miami Valley Market Hub, Inc.; NIPSCO Energy Services, Inc.; and PSRC Del., Inc.. MIIP is developing a system of natural gas market centers with high-deliverability salt cavern storage facilities that include the Moss Bluff facility in Texas, the Egan facility in Louisiana, and three other market hubs in various stages of development. The location of the project in Tioga, Pennsylvania, was selected based on gas market analysis and geological considerations. P. 529^