The unsteady heat flux from a non-reacting gas to the sidewalls of a channel has been determined during the piston compression of a single stroke. For small changes in the wall temperature, the heat flux may'be determined solely from the va.riation of the temperature outside the boundary layer or, alternatively, from the piston trajectory. Results for the heat transfer coefficient are also presented and exhibit a non-monotonic variation with respect to time.

T. Namba and T. Hiraoka, Zakum Development Company (ZADCO) SPE Member Abstract This paper shows that the horizons with finite vertical permeability can act as barriers for the injected water and prevent water slumping due to the effect of capillary force in a carbonate reservoir. The proposed concept 'capillary force barriers' can explain the various monitoring results consistently including the data obtained from pulsed neutron logs and dynamic testing tools. Introduction Thamama II reservoir of Upper Zakum Field is a Lower Cretaceous carbonate reservoir developed by five-spot pattern water injection. The open hole logs and pulsed neutron logs conducted in the observation wells indicate that the injected water is preferentially advancing in relatively thin horizons. The water slumping appears to be prevented by the underlying horizons. However, the core data do not show the existence of horizons which can be barriers within the reservoir. Furthermore, dynamic testing tools show the continuous pressure profiles, indicating that the reservoir is hydraulically connected. In this paper, the role of capillary force on water movement is highlighted. As studied numerically by Goddin et. al, capillary force accelerates crossflow in water-wet stratified reservoirs. However, in oil-wet reservoirs, capillary force can oppose crossflows of water as suggested by Willhite. It is shown in this paper that capillary force can prevent water slumping in the reservoir and the apparently inconsistent observations can be explained by introducing the concept of capillary force barriers. CONCEPT OF CAPILLARY FORCE BARRIERS The water-oil capillary pressure is defined as the pressure in oil phase minus the pressure in the water-phase, or (1) Thus, the capillary pressure can be either positive (water-wet) or negative (oil-wet) depending on the wettability preference. P. 41

The use of a simple data correction procedure which involves the adjustment of bottom-hole flowing pressure prior to a Pressure Fall-Off (PFO) test has been illustrated. The procedure has proved very effective for cases where the early time pressure data are marked by well bore secondary skin effects, which are commonly seen in high capacity water injection wells. The results of field cases considered, including those that may otherwise be considered as normal tests, showed that it is good Engineering practice to routinely apply the new procedure for all PFO tests in water injection wells. Introduction Pressure response profiles observable during PFO tests of water injection wells are sometimes very peculiar, offering no direct clues as to the predominant well bore phenomenon at early test times. This is more so for wells with limited perforations subjected to very high water injection rates. The pressure profiles of PFO tests on these wells are characterized by a substantial separation between the Pressure and the Pressure Derivative curves on the diagnostic (Log-Log) plots. Also the short time pressure response profiles are usually not amenable to analyses using established techniques for the flow regimes observable at short times. The long time pressure and derivative profiles are more descriptive. In view of the fact that PFO tests of water injection wells are of limited application in evaluating permeability of a given reservoir, it would appear that, in dealing with PFO tests of water injection wells, the emphasis should be on Interpretation with a view to understanding the fluid flow phenomenon at the near well bore region, and the reservoir rather than dwelling too heavily on routine analysis for reservoir parameters. We are therefore concerned with down-hole flow and static phenomena and their possible effects on reservoir dynamics involving such reservoir properties as average pressure and skin factors. In the circumstance, it is important that the short time pressure data be left unencumbered as much as possible so that all possible flow regimes can be evaluated without undue error. PFO in Water Injection Wells In order to meaningfully design or interpret a PFO test in a water injection well, it is important to understand, the factors governing the dynamics of this kind of test. We consider an injector at the center of a five-spot pattern. In its simplest form, we can assume that the water front moves radially outwards pushing the oil ahead of it. If we further assume that there is no interference between the injector and the producers within the pattern, we can in general expect to have three distinct zones within the drainage radius of the injector. These zones are made up of the following:A water swept region around the well bore where only water is flowing: designated as the water bank.An Oil/Water transition zone immediately ahead of the water bank where both oil and water are flowing.A virgin reservoir region of unswept oil where only oil is flowing designated as the oil bank.

During a laboratory waterflood study, undertaken at reservoir conditions to provide representative displacement data for predictive reservoir simulation studies, an investigation into acquiring representative wettability showed preserved samples exhibited significantly more oil wet character than restored samples. Further investigations concluded that core retrieval and/or storage resulted in increased oil wet character. Preserved state samples were not therefore representative. Introduction Pressure support into this giant oil reservoir is currently being achieved by water injection. It was originally predicted that water breakthrough would occur around the turn of the century. However breakthrough was observed in a number of production wells significantly earlier than had originally been predicted. A study was initiated to improve the understanding of the underlying causes of this water breakthrough. It was concluded that one of the key uncertainties governing the ability to predict waterflood performance was the quality of water/oil relative permeability data. Although there was a large number of historic water/oil relative permeability data sets, there was also a large degree of scatter in these data. This scatter appeared to be due, in part, to the variety of experimental procedures used. It was therefore unlikely that historic displacement data would be valid for reservoir performance. A process study was therefore initiated to generate new data using more rigorous procedures, including ensuring that samples in the laboratory were at a wetting state which was representative of the reservoir. This representative wettability was investigated by comparing displacement characteristics using plug samples in two wetting states at full reservoir conditions using in-situ saturation monitoring techniques. Technical Approach The approach for ensuring that a reservoir representative wetting state was attained in the laboratory compared displacement characteristics on samples prepared in two different ways, preserved state and restored state. Preserved state samples are samples which have not been cleaned with any solvents. Removal of any mud filtrate and saturation with brine is achieved by flushing with simulated formation brine, prior to initial water saturations being acquired. The preserved sample is then aged at full reservoir conditions for three weeks. Restored samples are samples which have been previously cleaned to as water wet state as possible. Samples are saturated with simulated formation bring and then, once initial water saturations has been acquired, are aged at full reservoir conditions with live crude oil. Prior to any reservoir condition studies it is essential to ensure that initial water saturations are acquired which are distributed uniformly down the length of the plug samples. This is necessary to ensure:Representative wettability is achieved during restorating/ageing at reservoir conditions with live oil.Representative Sor is obtained from the waterfloods because of the dependency on Sor with Swi.Non uniform Swi does not result in an unstable waterflood and nonrepresentative Sor.Trapped water (in strongly oil wet systems) does not cause an unstable flood and erroneous relative permeability data as well as suppressing initial oil permeabilities. As reservoir condition studies compare the displacement characteristics in preserved and restored samples, it is necessary to ensure that initial water saturations were successfully acquired in both preserved and cleaned samples.

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