University Block 31 Field Study: Part 2 - Reservoir and Gas-Plant Performance Predictions

Abstract

This paper presents projections of future reservoir and gas-plant performance of the University Block 31 Field. Modifications of the performance of the University Block 31 Field. Modifications of the compositional reservoir simulator to include surface operations of the Block 31 gas plant and fuel allocation procedures are described. Introduction Development of the history match for the University Block 31 Middle Devonian reservoir using a compositional simulator was presented in Part 1. In Part 2, a technique for projecting future performance is described, and the results of three projections are discussed.Numerous options in field operating procedures for the next 30 years can be analyzed and compared rapidly using a reservoir simulator. Among the questions concerning future reservoir performance that were considered are (1) What is the distribution and concentration of nonhydrocarbon gas in the reservoir now? In 10 years? In 20 years? (2) What is the effect of reservoir pressure level on ultimate recovery? (3) Will partial pressure level on ultimate recovery? (3) Will partial blowdown significantly hurt oil production rates and ultimate recovery? and (4) When should total blowdown begin?Concerning future gasoline plant production and fuel availability, the following questions are important (1) How rapidly does the Btu value of the various residue gas streams decrease in the future? (2) When will additional fuel be needed? (3) How long will a N2 rejection plant provide sufficient additional fuel? and (4) What quantity of plant product will be produced in the future?Much of this paper describes surface facilities because the operation of these facilities must be coupled with reservoir performance to make accurate long-term projections. Most decisions concerning changes in reservoir projections. Most decisions concerning changes in reservoir operations result directly from limitations of surface equipment. The most critical decisions are tied to the quantity and quality of the gas streams required for fuel. Fuel estimates involve the Btu quality and quantity of gas flowing from the reservoir and the ability of the surface equipment to bring the gas up to minimum fuel specifications.No economics are presented in this paper; therefore, no attempt has been made to select a "best" mode for future operations. The economics of each projection are subject to many constraints - i.e., U.S. gas and oil pricing regulations, which are likely to change with time pricing regulations, which are likely to change with time and which affect the conclusions drawn from any economic analysis. Surface Facility Calculations Gas Plant Operations Natural gas liquids are recovered at University Block 31 Field in a chilled, lean-oil absorption process. Three parallel absorbers are used, each operating at about parallel absorbers are used, each operating at about 1,100 psig (7.6 MPa). Fig. 1 shows the flow of the recovery process. Although temperatures vary slightly between absorber trains, the average gas inlet temperature to each absorber is about 15 degrees F 9.4 degrees C). The lean oil is chilled to about 30 degrees FThree rich-oil streams are combined and flashed at 650 psig (4.5 MPa). The liquid from this flash is fed to a psig (4.5 MPa). The liquid from this flash is fed to a rich-oil de-ethanizer (ROD). The bottoms from the ROD column are fed to the oil still, where the liquid products are separated from the lean oil. JPT P. 671