A Prospective Method to Increase Oil Recovery in Waxy-Shallow Reservoir
Waxy oil has been the main characteristics of The X field. Initial screening criteria studies indicated that cyclic steam stimulation (CSS) would be the optimum option because favorable reservoir condition. Based on this method we would like to know how much oil gain and the effect of steam for the stimulated and surrounding well. The injection of steam was done for 7 days followed by 14 days of soaking period. 39,000 liter of Marine fuel oil was used to generate steam for stimulation with an average produce steam quality about 80%. Average of 255 MMBTU of steam was injected each day with total steam injected was about 1.7 BBTU. The oil production was increased four times from 5 bopd into 21 bopd. Proper well candidate and high permeability are some reason for this method successfully increase oil production. Additional heat from steam reduced the damage near wellbore due to wax deposition. This is verifying by increasing productivity index from 3 bbl/psi to 4 bbl/psi. From results and observation data, this method can be a platform for typical shallow depth reservoir with high paraffinic content especially other reservoir in Sihapas formation.
Current Overview of Cyclic Steam Injection Process
Cyclic Steam Injection (CSI) is an effective thermal recovery process, in which, several driving mechanisms define the success of the process; i.e. viscosity reduction, wettability alteration, gas expansion, etc. This process was first applied in late 1950s. Then, it has been applied world-wide successfully to both light and heavy oil reservoirs. To increase the effectiveness of CSI, process was varied by chemical addition to steam, application of horizontal wells and introduction of hydraulic fracturing. With these modern technologies, average 15% of recovery factor of conventional CSI producers back in 1980’s boosted up to approximately 40%. The method is attractive because it gives quick payout at relatively high success rate due to cumulative field development experiences. However, this is still uncompetitive in terms of ultimate recovery factor compared to that of other steam drive methods such as steam flooding (50-60% OOIP) or SAGD (60-70% OOIP). Recent studies related to the CSI have focused on either the optimization of chemical additives and fracture design or questioning on geomechanical solutions to poroelastic effects. In addition, most papers discuss about follow-up process posterior to CSI such as in-situ combustion, CO2 injection and steam flooding. This study is oriented to overview of the past and current status of CSI process in technical aspects with discussion of commercial cases throughout the world. A summarized review is given on the potential importance of encouragement of further investigation of Cyclic Steam Injection.
Estimation of geological formation thermal conductivity by using stochastic approximation method based on well-log temperature data
Thermal conductivity is a key parameter for evaluating wellbore heat losses which plays an important role in determining the efficiency of steam injection processes. In this study, an unsteady formation heat-transfer model was established and a cost-effective in situ method by using stochastic approximation method based on well-log temperature data was presented. The proposed method was able to estimate the thermal conductivity and the volumetric heat capacity of geological formation simultaneously under the in situ conditions. The feasibility of the present method was assessed by a sample test, the results of which shown that the thermal conductivity and the volumetric heat capacity could be obtained with the relative errors of −0.21% and −0.32%, respectively. In addition, three field tests were conducted based on the easily obtainable well-log temperature data from the steam injection wells. It was found that the relative errors of thermal conductivity for the three field tests were within ±0.6%, demonstrating the excellent performance of the proposed method for calculating thermal conductivity. The relative errors of volumetric heat capacity ranged from −6.1% to −14.2% for the three field tests. Sensitivity analysis indicated that this was due to the low correlation between the volumetric heat capacity and the wellbore temperature, which was used to generate the judgment criterion.