Abstract

A multiple-well test was conducted in Oklahoma which enabled the identification of two separate reservoirs in a new field. Quantitative analysis of the test, including determination of well-to-well permeability and distances to reservoir boundaries, was done using an analytical multi-well reservoir simulator. The test results were used to help determine whether additional wells were needed to optimize primary recovery for the field.

Introduction

Multiple-well tests yield valuable information for reservoir characterization and thus provide an important aid to reservoir management. Whereas single-well tests yield information about reservoir pressure, permeability, the model of the reservoir and the wellbore damage condition, multiple-well tests provide a view of the entire reservoir system on a much larger scale. Multiple-well testing provides information about interwell reservoir properties, the degree of communication between different wells, and information about reservoir heterogeneity. The production engineer integrates the knowledge gained from multiple-well tests with geologic information, cores, logs and other data to improve the overall description of the reservoir and aid in all phases of reservoir management. In the primary recovery phase, multiple-well tests aid in well spacing and unitization design and in pressure maintenance decisions for the field. During secondary and enhanced recovery phases, multiple-well testing is used to design and monitor injector and producer flood patterns, and to learn about and monitor directional trends in the reservoir.

A field example is presented which demonstrates a practical application of multiple-well testing. A six-day test involving four wells was conducted in the Mid-Continent area to quantify communication across a new field.

Interpretation and Modeling

Multiple-well tests are conducted by monitoring the pressure response at an OBSERVATION well while transients are created at one or more ACTIVE wells. The problems inherent in conventional interpretation of multiple-well tests are that some of the prerequisites for the interpretation are impractical or even impossible. For instance, the industry- accepted technique for analyzing multiple-well tests makes the assumption that the observation wells will be at static reservoir conditions both before and during testing. Thus, in many cases, it would be necessary to shut in the observation wells long before the proposed testing in order to meet that requirement. Also, it is assumed that there will be only one active, or interfering, well. This would often make it necessary to shut down operations in many surrounding wells. Additionally, conventional analysis usually assumes that the reservoir is homogeneous and radially infinite. These limitations have made it difficult to conduct and interpret multiple-well tests.

Multi-Well Reservoir Simulator

An analytical multi-well reservoir simulator was developed to enable a more practical and realistic method of conducting and interpreting multiple-well tests. This simulator uses superposition in space to allow interpretations with any number of active wells. Additionally, superposition in time is used to account for production and/or injection at all wells, so even the observation well can be "active." Finally, the simulator also models other reservoir types, such as two-porosity, as well as outer boundary conditions, such as a single sealing fault, channel or closed rectangle geometry.

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