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O PERATING systems manage a computer's resources, maintain its permanent data, and provide an efficient environment for the execution of user programs. Users expect an operating system to provide a certain level of resilience to failure and facilities for recovering from failure with minimal interruption of computations and minimal loss of data.In conventional operating systems, these tasks are centered around the file system as the repository of permanent data and virtual memory as the execution environment. Persistent systems offer an alternative view in which the lifetime of data is separated from the access mechanism. In a persistent system, all data, regardless of its lifetime, is created and manipulated in a uniform manner.When persistence is included as the basic abstraction of an operating system, many of the inadequacies of existing operating systems are eliminated and the tasks of an application J o h n R o s e n b e r g , A l a n D e a r l e , D a v i d H u l s e , A n d e r s L i n d s t r ö m , a n d S t e p h e n N o r r i s OPERATING SYSTEM SUPPORT FOR PERSISTANTand RECOVERABLE COMPUTATIONS Guaranteeing data recovery and consistency, the authors' experimental Grasshopper persistent operating system simplifies application development and encourages construction of integrated systems.

In a previous paper we described the laboratory work, reservoir simulation, and initial design of a CO2 Foam Pilot in the Salt Creek Field, Natrona County, WY. In this paper, we review the diagnostic testing and initial results from the pilot including: injection rate profile, production data analysis, injection and production logging, chemical tracers, streamline analysis, and reservoir simulation. Although the CO2 flood has been very successful at Salt Creek, it is recognized that certain isolated patterns have exhibited high CO2 production and inefficient CO2 utilization, most likely due to the channeling of fluids through high permeability, low volume zones (fractures, thief zones, etc.) and the gravity over-ride of the injected fluids. Accordingly, a foam pilot was initiated to test the ability of CO2 to remediate these conditions. A change in the injection well rate (at constant surface injection pressure) was the first indicator to be observed; the injection rate decreased by approximately 40%, indicating a strong mobility reduction of the CO2 in the reservoir. Production and injection profile logs were run before and after surfactant injection, and a change in profile was observed in one producer. Chemical tracers were injected in both the gas and water phases before and after surfactant injection; results indicate that CO2 was diverted from high permeability, low volume conduits, such as fractures. An analysis of the production data for the four offset producers show a definite increase in liquid production and a corresponding decrease in GLR (gas-liquid-ratio.) Streamline analysis suggest areal diversion of CO2 over time. Finally, reservoir simulation prediction cases are given and discussed. CO2 flooding has become a standard EOR technique for many water-flooded fields. Methods for increasing the efficiency of these floods, such as the use of CO2 foam, can add great value.

The 1992 SPE PETROLEUM COMPUTER CONFERENCE introduced a new concept, the SOFTWARE SHOWCASE. This new program is intended to be similar to the "COMPARATIVE SOLUTIONS IN RESERVOIR SIMULATION" project that has been a popular feature of the SPE Symposium in Reservoir Simulation for a number of years. The Program Committee chose pressure transient analysis software as the SHOWCASE topic for the initial outing. A total of four (4) problem sets were developed from actual field data-sets from CONOCO and TEXACO. Ten vendors and service companies answered the call for papers and the results of their efforts are presented in this paper. We should point out that there is no "correct" or "unique" to the four sample problems based upon the information furnished to the participants. The overall intent of this paper is NOT to present either a direct or implied endorsement of any one software product but to spur spirited discussion in the are of well testing software and to provide a service to SPE members who might be involved in the evaluation of transient pressure analysis programs.