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Knowledge of initial-residual saturation values are required to estimate recovery efficiency and the economic viability of an oil recovery project. Accurate knowledge of the oil content of a reservoir is critical in the economic evaluation of any prospect for enhanced oil recovery after conventional recovery by primary means and any injection of water and gas. The accuracy of these data is very critical for implementing post-waterflood techniques because project economics are very sensitive to oil saturation in a partially depleted reservoir. Consequently, attempts have been made to determine oil saturation values from various techniques. However, the commonest and most economical method has remained the routine analysis from cores cut with water-base muds. But these render inaccurate results due to inherent flushing during coring as well as oil shrinkage and expulsion due to gas expansion during core lifting to the surface. Typically, such results are corrected for shrinkage and the resulting value is arbitrarily increased again by a bleeding factor of 10%–15%. There are no published industry correction data to correctly account for flushing and blowdown in conventional cores. This paper presents the core analysis results of a highly controlled, bland water-base sponge coring program with a PDC maximum-flushing corehead designed to simulate a waterflood The results from 29 full-diameter core analysis from 200 feet of recovered core yielded an average bleeding / expulsion factor (E) of 1.062 which we believe to the first such published data set to provide a measured E factor for correcting residual oil saturation values from conventional cores. The results are supported by a well designed and properly implemented quality control program. The results of the sponge coring program also compare very well with residual oil determined from other sources. Introduction Oil saturations determined from analysis of cores that are cut with water-base muds are always less than in-situ saturations because of drilling-fluid invasion and oil flushing during coring, and oil shrinkage and expulsion due to gas expansion as the core is lifted to the surface. The core is subjected to pressure and temperature reduction as it is brought to the surface. Thus, the gases released from solution with pressure decline cause shrinkage of the oil volume, and as the gases expand and escape from the core, they expel some of the core fluids. Use of pressure-retaining core barrel or sponge coring techniques can eliminate this second effect but do not eliminate flushing. Two well-known flow processes can occur to cause oil flushing during core cutting and retrieval:mud filtrate invasion caused by overbalance pressure at the drill bit during coring operations andfluid expansion caused by a drop in pore pressure during core retrieval. Jenks et al provided information indicating that overbalance pressure is the prime factor in oil stripping during coring operations. Consequently, accuracy in reserves determination requires that residual oil saturations be corrected for the effect of high pressure gradients around a wellbore which can arise during both drilling and production. Rathmell et al point out, however, that routine core analysis oil saturations that are adjusted for bleeding and shrinkage, can give reliable values for residual oil saturation after waterflooding in many sandstone reservoirs, particularly those containing low-viscosity oils. However, Rathmell and group have not provided a correction factor value for adjusting the oil saturations for bleeding and shrinkage. In consideration of this problem, Kazemi proposed the following equation: (1) P. 445^

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Recent studies have suggested the possibility of spontaneous emulsification as a mechanism for enhanced oil recovery (EOR). The discussions have, however, remained essentially qualitative. A study was therefore undertaken to estimate quantitatively the contribution of spontaneous emulsification as an EOR mechanism. The tests were conducted on several bulk liquidlliquid systems as well as by displacement experiments in unconsolidated synthetic sand packs. Spontaneous emulsification was found to be a mechanism for EOR: the estimated extra contribution to EOR due to this mechanism was found to be significant in laboratory scale displacement experiments. Tertiary recovery was always greater when spontaneous emulsification was evident than otherwise. Results of tests on bulk liquidlliquid systems indicate that the occurrence or absence of spontaneous emulsification can be correlated with the values of 'partition parameter'. It may be concluded that higher oil recoveries may be achieved in chemical EOR processes where interface mass transfer (and the accompanying spontaneous emulsification) occurs. The evaluation of efficiency of residual oil mobilisation through the capillary number theory (with and without spontaneous emulsification) is also discussed. Displacement tests with spontaneously emulsifying systems showed that residual oil left behind a conventional waterflood was mobilised in a range of capillary numbers much less than that which applies to low-tension waterfloods.

The Dulang field discovery wells were drilled by PETRONAS Carigali Sdn Bhd, (Carigali) and Esso Production Malaysia, Inc., (EPMI) during 1981 -82 in their respective portions of the field. Results of seismic interpretation and subsequent appraisal drilling, revealed an extensive, east-west trending, complexly faulted anticline plunging westwards. It was recognized early that the optimal field development plan mast be predicated on an integrated reservoir description spearheaded by the acquisition of 3-D seismic data to accurately define the structure.Early data indicated that both fluid and pressure communication existed between the EPMI and Carigali sections of the field. Unitization was inevitable and the agreement was reached in 1988. Carigali was appointed operator of the Unit Area. This paper describes the application of an integrated multidisciplinary approach to the development of the Dulang oil field offshore Peninsular Malaysia. The staged development of this complex field, with two of the planned total four platforms currently onstream, is an _ innovative approach to offshore development, involving synergism of disciplines, and placed a premium on flexibility in approach. The practical issue addressed was the full utilisation of available information and expertise, involving the full range of geophysical, geological, and engineering expertise, to ensure optimum field development on schedule and on budget. The major issue in field development at the Dulang oil field was that of reservoir description. seismic interpretation, even with a high degree of well control, was complicated by the presence of shallow gas and dense faulting. Continuous geological reviews were able to resolve reservoir structure and lithology beyond that provided by applied geophysics. Engineering analyses of pressure data identified fluid contacts and established interwell continuity. Uncertainties in petro physical properties are being addressed by a special drilling and core recovery program involving the use of bland water-base and bland low-toxicity oil-base muds, advanced reservoir mechanics analysis and integrated log analysis programs. An integrated reservoir study of the Dulang field is ongoing, and comprises comprehensive analyses of the geology, petro physics,

Recent studies have suggested the possibility of spontaneous emulsification as a mechanism for enhanced oil recovery (EOR). The discussions have, however, remained essentially qualitative. A study was therefore undertaken to estimate quantitatively the contribution of spontaneous emulsification as an EOR mechanism. The tests were conducted on several bulk liquid/liquid systems as well as by displacement experiments in unconsolidated synthetic sand packs. Spontaneous emulsification was found to be a mechanism for EOR: the estimated extra contribution to EOR due to this mechanism was found to be significant in laboratory scale displacement experiments. Tertiary recovery was always greater when spontaneous emulsification was evident than otherwise. Results of tests on bulk liquid/liquid systems indicate that the occurrence or absence of spontaneous emulsification can be correlated with the values of ‘partition parameter’. It may be concluded that higher oil recoveries may be achieved in chemical EOR processes where interface mass transfer (and the accompanying spontaneous emulsification) occurs. The evaluation of efficiency of residual oil mobilisation through the capillary number theory (with and without spontaneous emulsification) is also discussed. Displacement tests with spontaneously emulsifying systems showed that residual oil left behind a conventional waterflood was mobilised in a range of capillary numbers much less than that which applies to low‐tension waterfloods.

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