Monarch Sandstone: Reservoir Description In Support Of A Steam Flood Section 26C, Midway-Sunset Field, California
Authors: Webb M.G. 
Published: March 2010

Study of the Monarch sandstone in the vicinity of the 26C Steam Flood Field Trial shows the sand to consist of a series of turbidites which have experienced contemporaneous structural deformation and subsequent erosion. Knowledge of the local basin topography at time of deposition allows a prediction of permeability orientation to be made.

A reduction in vertical permeability associated with diatomites deposited between turbidites is noted. The preservation of these diatomites is related to the erosional energy possessed by subsequent flows.

Quiescent periods during deposition of this sequence deposited thick diatomites in some areas of the field. The mapping of these diatomite "swarms", together with the inferred permeability orientation, allows a prediction to be made regarding the behaviour of the injected fluid in the subsequent steam flood.

Introduction

The Monarch sandstone in section 26C, 32S, 23E, Kern County, California, was placed on steam drive in November 1975 after an extended period of primary production and cyclic steam-enhanced recovery. Prior to steam injection, cores were obtained from wells 26C 0–1 and 26C 0–2, which were drilled as temperature observation wells (Fig. 1) and cored both as an aid to better reservoir description and to evaluate coring methods in unconsolidated sandstone, A third well, 26C- 0–3, was also completed as an observation well. Well 26C 0–3 is on strike with injector 67W; 0–2 and 0–1 are respectively farther updip.

The steam flood field trial was designed to test steam drive in a steeply dipping (10-degree), thick (300 feet), heavy oil reservoir. Reservoir and fluid characteristics are summarized in Table 1.

Gomaa, Duerksen and Woo (1976) detailed the first attempts at predicting the pilot performance using Intercomp's steam flood simulator. A companion paper (Duerksen, Gomaa, 1977) addresses the progress of this flood and documents field evidence for the validity of this reservoir description.

The reservoir description is approached with steam drive in mind, cognizant that gravity override is the major concern in steaming thick zones.

Regional Structures, Unconformities

The 26C steam flood pilot is located on the southwest flank of the SpelIancy anticline (Fig. 2), a portion of the Midway-Sunset field. The structural axis strikes ENE; theanticline plunges ENE at 6 to 7 degrees. Dip on the SEflank of the pilot area is =10 degrees.

The Monarch sandstone averages = 350 feet thick over the field trial area. Two major unconformities truncate the sandstone (Fig. 2). The post-Pliocene Etchegoin unconformity erodes the Monarch over the crest of the structure; the Pleistocene Tulare unconformity causes an even more abrupt truncation to the SW. In the area of the field trial, the Monarch is free of erosional and faulting effects, excepting the most updip portion.

General Stratigraphy

The Monarch saindstone is the arenaceous equivalent of the silty, and diatomaceous Antelope shale. It is of Upper Miocene, Upper Mohnian age and is correlated with the Stevens sand to the northwest. Elsewhere in Midway-Sunset it may be called the Spellancy Sand or the Marvic.