A.S. Emanuel

Design and Evaluation of a Nitrogen-Foam Field Trial

The paper describes the planning, implementation, and evaluation of an N{sub 2}-foam filed trial at the Painter reservoir in Wyoming. Foam properties of a proprietary surfactant were measured in corefloods at reservoir conditions and modeled with an empirical foam simulator. Foam injection into a dual injector/producer temporarily reduced injectivity but was ineffective in controlling N{sub 2} channeling.

Pseudo-relative permeability for well modeling

Several authors have described the use of pseudo-relative-permeability curves for modeling the vertical performance of formation flow in areal reservoir simulators. The pseudo curves are usually determined from small cross section or 3-dimensional models and then incorportated into large-scale areal models. The concept of pseudo-relative permeability also can be extended to the vertical performance of individual wells by a technique analogous to that for formation flow. Pseudo-relative-permeability curves can be obtained for each well by running a cross section model through the expected range of pressure and production in the same way that interblock pseudo-relative permeability is derived. At each time step, the equations given yield one point on the pseudo curve. An example shows a 7-layer cross section model with 4 producing wells.

Fractal Methods Improve Mitsue Miscible Predictions

A reservoir modeling technique based on fractal geostatistics was used to interpret the displacement processes and to predict the response to a miscible-hydrocarbon water-alternating-gas (WAG) flood in a major portion of the Stage 1 project area of the Gilwood sand in the Mitsue field. The purpose was to compare projections based on geostatistical techniques with those based on conventional modeling and to compare the accuracy of the projections with current field measurements. Results indicate that a hybrid finite-difference/streamtube technique based on fractal representations can provide a full project model for an efficient expenditure of effort and computer time. Individual well response is predicted qualitatively. Analysis of tracer breakthrough and production logs agree with the solvent/water flow patterns predicted by the fractal model.

Laboratory Study of Foaming Surfactant for CO2 Mobility Control

The effectiveness of foam as a mobility-control agent has been tested by an immiscible CO/sub 2/ coreflood displacement of a California heavy oil (14/sup 0/API (0.97 g/cm/sup 3/)). Foam was produced by simultaneous injection of 0.5 wt% surfactant solution and CO/sub 2/. Foam injection recovered an incremental 33.6% of original oil in place (OOIP) by reducing CO/sub 2/ mobility and diverting CO/sub 2/.

A Laboratory Study of Wilmington Tar Zone CO2 Injection Project

The authors conducted a laboratory study of heavy-oil recovery by CO/sub 2/ injection to support the Wilmington, CA tar zone CO/sub 2/ injection project operated by Long Beach Oil Development Co. The study comprised (1) phase behavior of Wilmington tar zone reservoir oil and CO/sub 2/, and (2) phase behavior of the oil and the refinery gas used for the field project, (3) viscosity measurements of oil/gas mixtures, (4) reservoir-condition displacements of oil by CO/sub 2/ and by refinery gas, (5) equation-of-state characterization of phase behavior, and (6) computer simulation of gas/oil displacements. Saturation pressures and swelling factors were measured for oil/gas mixtures, which showed that N/sub 2/ is substantially less soluble in oil than is CO/sub 2/. Viscosity measurements show that the viscosity reduction is a function of pressure and of the total gas dissolved in the oil. Four reservoir-condition corefloods showed that the recovery efficiency of CO/sub 2/ is higher than that of the refinery gas for continuous or low WAG injection, and the recovery efficiency of the refinery gas at 1:1 WAG is about twice that of continuous injection. The corefloods were modeled with a finite-difference compositional simulator. Predictions agree with the experimental results.

Reservoir studies with geostatistics to forecast performance

In this paper example geostatistics and streamtube applications are presented for waterflood and CO{sub 2} flood in two low-permeability sandstone reservoirs. Thy hybrid approach of combining fine vertical resolution in cross-sectional models with streamtubes resulted in models that showed water channeling and provided realistic performance estimates. Results indicate that the combination of detailed geostatistical cross sections and fine-grid streamtube models offers a systematic approach for realistic performance forecasts.

Solution of Pressure Equations for Large Reservoir Models Using Block Successive Overrelaxation and an Array Processor

Block successive overrelaxation (SOR) is used to solve the pressure equations of large 3-dimensional reservoir models with limited or zero permeability between layers. The equations for each block are solved simultaneously using sparse elimination techniques. The block technique shows two or three times better convergence than plane SOR. Two hypothetical test problems and three reservoir problems ae described. 8 refs.