History Matching of Heavy-Oil Production for Comparing New Approaches to Generating Reservoir Property Distributions, West Coalinga Field, California

Abstract

Reservoir simulation of steam injection into heavy oil sands of West Coalinga Field in California has been conducted to assess suitability of different permeability distributions generated from geological and fractal modeling processes. Permeability distributions in each model were derived by integrating stratigraphically controlled models with core data provided by Chevron Production Company. Three distinct distributions were generated for each lithologic group: facies tract, facies group, and a fractal distribution of the facies group. The grid design is based on stratigraphic architecture of depositional facies. Construction of these models involved application of advanced analytical property-distribution methods conditioned to continuous outcrop control for improved reservoir characterization. Numerical simulation of steam injection into three adjacent 5 spot well configurations was used to assess suitability of each model. Injection and production histories of wells in the study area were simulated, including shutdowns and the occasional conversion of production wells to steam injection wells. The framework provided by the facies groups yielded a more realistic representation of reservoir conditions than facies tracts, which is revealed by a comparison of history-matching results. Permeability distributions obtained using the fractal model predict the high degree of heterogeneity within reservoir sands of West Coalinga Field. Modeling results indicate that predictions of oil production are strongly influenced by the geologic framework and by the boundary conditions. Improved predictions of interwell reservoir heterogeneity have the potential to increase productivity and to reduce recovery cost for California's heavy oil sands, which contain several billion barrels of reserves in the San Joaquin Valley. Introduction The West Coalinga oil field in California (Figure 1) produces from heavy oil sands of the Miocene Temblor Formation. The oil in this field has low API gravity (12º to 15º API) and is highly viscous at the 40ºF initial reservoir temperature. This makes the field an ideal candidate for enhanced oil recovery through steam injection. The field is shallow, multilayered and stratified with low reservoir pressure, varied rock permeability, and an average porosity of about 34%.[1] Steamflooding started in 1961, and Coalinga is the oldest steamflood operation in the state of California. Prior to 1960, only about 10% of the oil in place was produced, but with the advent of steam floods and horizontal drilling, recoverable oil potential has been increased up to approximately 60 to 70%. West Coalinga field was chosen for this study because of the opportunity to relate continuous cores of the producing Temblor Formation to nearby outcrops of the same formation. Observations of lateral variability and vertical sequences in outcrop led to an improved understanding of the geological framework of the reservoir. In particular, detailed characterization of stratigraphic bounding surfaces in outcrops enabled identification of those same surfaces in cores and logs of the reservoir. The bounding surfaces were subsequently used as reference horizons in reservoir modeling.

Extraction of Energy Resources—Exploitation of the Canadian Oil Sands

“…This centrifuge process was further improved by incorporating a gravity-settling device to scalp some of the oil, thereby reducing the reliance on the centrifuge units. This improvement was incorporated into circuits in the early 1980s [12].…”

“…The composition of the diluent will tend to control the dissolution of bitumen. By this action, the diluent reduces both the density and viscosity of the hydrocarbon phase, resulting in a high product quality (94% to 95% hydrocarbon) at high recoveries (~98%) [12].…”