Gravity Segregation in a Propane Slug-Miscible Displacement Project-Baskinton Field, Louisiana

Abstract

Abstract A propane slug-miscible displacement project was instigated in Baskinton field, Franklin Parish, La., in April, 1962. Laboratory tests and potentiometric studies were performed to insure applicability of the miscible displacement mechanism to this reservoir. As the principal part of the evaluation of this project, an observation well was drilled in the reservoir near the injection well. From this well, a three-string triple completion equipped with separate surface gas and oil measuring facilities, token withdrawals were produced in an attempt to examine and define frontal profiles. Introduction Many miscible displacement projects of the LPG-slug type have been undertaken and various degrees of success reported in the literature. "Premature" or early breakthrough seemed a common difficulty in these projects. Sun felt that the reservoir rock properties of the Holt "D" sand would permit a true test of gravity segregation in a lowdip reservoir as the homogeneity minimized the effects of permeability distribution. Equally as important was the thought that an examination of frontal profiles would permit an evaluation of mixing-zone performance. The following pages discuss the design and subsequent performance of an observation well drilled expressly to collect data on the propane slug-miscible displacement project. This paper is an interim report on this project. Comments on preliminary results regarding mixing zone description and displacement efficiency are included, but no definite conclusion in these areas can be drawn at this early stage of the project. Geology and Reservoir Characteristics Baskinton field, La., is located several miles south of Delhi, La, (and the Delhi field) in the northeastern corner of the state. The Holt "D' sand, the horizon of interest in this project, is a stratigraphic trap encountered at 3300 n. As depicted on Fig. 1, the trap strikes generally East-West and is bounded on all sides by a pinchout, except on the south side where a water-oil contact establishes the reservoir limits. The sand is very low relief, dipping generally to the South at about 2 degrees. It is a well developed homogeneous Lower Tuscaloosa sand of Cretaceous age. The reservoir originally contained approximately 5 million STB of oil. Table 1 shows the rock and fluid characteristics of the reservoir. Primary Performance and Pressure Maintenance Investigations From discovery in mid-1956 to Jan. 1, 1962, the field produced 525,000 STB of oil, 275,000 Mcf of gas and 6,000 bbl] of water. A pressure decline of 150 psi from the original of 1,802 psig accompanied this production. A material-balance calculation, supported by field performance, indicated the presence of a partial water drive aiding the dissolved gas drive mechanism in this reservoir and impeding the formation of an adverse gas saturation. Pressure maintenance possibilities involving water injection and propane slug-miscible displacement were subjected to detailed engineering analyses. Sweep patterns for each, subject to conventional potentiometric analyzer limitations, were determined. In the propane-slug potentiometric study, injection in a Single up-dip well near the pinchout yielded an essentally radial pattern. This will become quite significant later in the discussion. The propane-slug program appeared economically more attractive than the water-injection program and was selected as the pressure maintenance mechanism. JPT P. 661ˆ