University Block 31 Field Study: Part 1 - Middle Devonian Reservoir History Match
Authors: Warner H.R. , Hardy J.H. , Robertson N. , Barnes A.L. 
Published: December 2007

University Block 31 Field Study: Part 1 - Middle Devonian Reservoir Part 1 - Middle Devonian Reservoir History Match

This paper describes the use of a compositional reservoir simulator to match a suite of PVT experiments and laboratory tube displacements for the high-pressure, gas-drive process. A history match of 30 years' performance of more than 100 wells, including both lean- and flue-gas injection, is presented. presented. Introduction

Performance of the Block 31 Middle Devonian reservoir Performance of the Block 31 Middle Devonian reservoir was analyzed. This study provided the field engineers with a working tool for evaluating future reservoir performance. This study also provided gas-plant performance. This study also provided gas-plant personnel a method for predicting future gas-plant production personnel a method for predicting future gas-plant production and fuel availability.A compositional simulator' was used in this study. With this type of simulator, compositional effects were accounted for and the gas-plant performance was simulated. Previous studies of this reservoir using black-oil simulators gave poor history matches. Black-oil models cannot calculate the gas-plant performance needed to make long-term projections. By modeling the entire Middle Devonian reservoir, the possibility of incorrect no-flow boundaries that plagued previous pattern area analysis of this field was eliminated. pattern area analysis of this field was eliminated. The steps required to develop the history match of the reservoir performance are described here. This includes initialization of the model, testing of the compositional simulator's ability to mimic the high-pressure, gas-drive displacement process, and the philosophy used to obtain an acceptable history match. Part 2 describes the model modifications required to expedite the projection computations and three projections of future field performance and gas-plant operations. performance and gas-plant operations. Reservoir Description

The Block 31 (Devonian) Unit is located 9 miles (14.5 km) northwest of Crane, TX. The structure on top of the Devonian is a northeast-southwest trending anticline (Fig. 1) bounded on the south and southeast by normal faults. Productive area is 7,840 acres (31 × 10 M).

The Devonian interval has three reservoirs: Upper, Middle, and Lower (Fig. 2). The major reservoir is the Middle at 8,500 ft (2590 m) [- 6,000 ft (- 1828 m) subsea] and its net pay averages 170 ft (51.8 m). The Devonian pay consists of 65% tripolitic chert and 20% fine crystalline, sucrosic limestone. The remainder is variable amounts of lime mud, skeletal material, pellets, and quartz silt. The porosity is intercrystalline and averages 15%. The permeability averages 1 md, but is 8' to 10 times this amount in the hairline fractures present in the reservoir. Table 1 lists pertinent reservoir parameters. parameters. History

ARCO Oil and Gas Co. discovered the Block 31 Field in 1945. Partial pressure maintenance was begun in 1949 by reinjecting produced gas. In 1952, the field was unitized for full pressure maintenance. Other companies in the unit are Phillips Petroleum Co., Champlin Petroleum Co., and Continental Oil Co. Petroleum Co., and Continental Oil Co. Beginning in 1955, the high-pressure, gas-drive process was used in the Block 31 Middle Devonian process was used in the Block 31 Middle Devonian reservoir.

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