Simulation and Design of Steam Drive in a Vertical Reservoir
Authors: Moughamian J.M. , Woo P.T. , Dakessian B.A. , Fitzgerald J.G. 
Published: December 2007

A three-dimensional (3D) simulation model was used to design steam drive in a steeply dipping (53 deg.) heavy-oil reservoir in California and to select the optimal well pattern from eight alternatives. Sensitivity runs were made to study selected reservoir and operating parameters. The results show that upstructure injection with a modified staggered pattern results in increased recovery. Injection rate, steam quality, and formation dip are important parameters. Permeability normal to the bedding plane has little effect. Grid orientation affects oil recovery efficiency but does not change the optimal well pattern that was selected.

Introduction

The Webster sand sequence in the Midway-Sunset field is an attractive candidate for steam drive. The sands are unique because of their steep dip (53 deg.). It was recognized that placement of injection would be critical. Initial planning addressed the question, "What would be the optimal well pattern for this steeply dipping reservoir?" A three-dimensional, finite-difference, steam-injection simulator was used to assist in answering this question. This paper describes the reservoir and its geology, the brief production history under primary depletion and cyclic steam injection, and the results of the simulation study. Based on this study, a steam-drive project has been designed. A drilling and completion program for the project is under way, and steam injection is scheduled for mid- 1982.

Reservoir Characteristics Geology

The section 2F Monarch lease (220 acres) is situated in the southern portion of the Midway-Sunset field near the town of Maricopa, CA. The main productive horizon is the Webster sand sequence at an average depth of 1,200 ft. The Monarch sand has limited development and is separated from the Webster sand by a fault. The Webster sand series (Upper Miocene) consists of turbidites and submarine fan deposits separated by numerous thin and discontinuous diatomaceous shale beds. The sands are divided into five main units (A, B, C, D, and E) and are thickest near the center of the property. The average stratigraphic thickness of each unit is 100 ft. The beds dip an average of 53 deg. northeast and are truncated updip by a gently dipping Pliocene unconformity. Fig. 1 shows a typical induction-electric log.

Rock and Fluid Properties

The Webster sand is unconsolidated, poorly sorted with fine to coarse grains, and conglomeratic in part. Core analysis showed that porosity is 21 to 28% and air permeability is 1,200 md under reservoir conditions. The sand is saturated with a 14 deg. API oil, whose viscosity is a strong function of temperature. Table 1 is a summary of rock and fluid properties used in the simulation. Water/oil and gas/oil relative permeabilities of Webster sand cores at reservoir temperature were measured and plotted in Figs. 2 and 3, respectively. Temperature-dependent endpoints of the relative permeability curves given in Table 2 were either measured or estimated from published data.

Production History

The Midway-Sunset field was discovered in the early 1890's. The initial development of Section 2F began in 1917. Primary production continued until about 1960 when it became uneconomical. By that time, cumulative production from the Webster sands was 2.3 MMSTB, and the production rate was 120 BOPD. Cyclic steaming on Section 2F started in 1965 with good response.

JPT

P. 1546^