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This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 91755, "Fast Method Finds Infill-Drilling Potentials in Mature Tight Reservoirs," by L. Guan, SPE, Texas A&M U., and Y. Du, SPE, New Mexico Inst. of Mining and Technology, prepared for the 2004 SPE International Petroleum Conference in Mexico, Puebla, Mexico, 8-9 November.
Abstract Infill drilling has been identified to play an important role in improving oil or gas recovery in the tight hydrocarbon fields. But quantifying the infill drilling potentials in producing tight hydrocarbon fields is often a challenging problem, due to large variability in rock quality, well spacing, well completion practices, and the large number of wells involved. At the same time, with the increasing demand for energy and favorable oil and gas prices, more and more fields all over the world are undergoing infill drilling. It is not uncommon for a company to have hundreds or thousands of infill candidates to choose from. Complete integrated reservoir studies to determine infill potential are often very time-consuming and costly for many tight hydrocarbon fields. This paper presents an alternative approach to conduct detailed reservoir studies to find infill drilling potentials in tight hydrocarbon basins. This method can quickly evaluate the infill drilling potentials within weeks even with thousands of wells. Several field examples are provided to demonstrate the application of the method in mature-tight gas basins and the primary advantages of the technique are its speed and reliance upon well location and production data only. Introduction As the world's supply of conventional oil and gas reservoirs begins to deplete in the 21st century, the world will demand that oil and gas production from unconventional reservoirs increase to help supply keep up with demand. One of the keys to ensuring an abundant, economical, and environmentally-friendly supply of natural gas is developing the tremendous gas resources in unconventional, low-permeability, tight reservoirs. Although the average production rate of gas wells from the unconventional, low-permeability, tight reservoirs is low, they still play an important role in the petroleum industry. According to the 2003 released Interstate Oil and Gas Compact Commission (IOGCC) survey, the tight gas wells collectively represent 10 percent of the natural gas produced onshore in the lower 48 states which accounts for 43 percent of the overall rise in natural gas production over the year 2002, and tight oil production increased by 7,678,000 barrels in 2002 to 323,777,000 barrels while the overall domestic onshore oil production declined. However, the low-permeability wells are being produced not by major oil companies, for the most part, by small independent operators. Research is the key to the survival of those low-permeability wells; however, those small independent producers do not have the means to conduct their own research. Faced with the daunting task of trying to determine where to drill several hundred infill wells in a tight-gas reservoir, many operators have to rely on very simple analyses to select infill locations. This often results in wells being drilled in the wrong locations, and even worse, after seeing less-than-expected infill performance, many operators will simply give up on infill drilling and this may be missing significant opportunities. Infill drilling of additional wells after initial development (primary and/or secondary) played an important role in improving the oil and gas recovery in the tight hydrocarbon reservoirs. Generally speaking, the reservoir heterogeneity and layer continuity can be changed by the well spacing. The infill drilling wells reduce the well spacing of the hydrocarbon fields and then enhance the well connectivity. Wu, et al. reported the results of their study to determine the impact of infill drilling on the waterflood recovery in West Texas carbonate reservoir. Their study shows a certain degree of correlation between the waterflood recovery and well spacing. Recently, with the increasing demand for energy and favorable oil and gas prices, more and more fields all over the world are undergoing infill drilling. Although the advances in reservoir management provides a much clear picture of hydrocarbon distribution in the reservoirs which helps petroleum engineers to plan highly effective well profiles. The advanced imaging technologies allow the hydrocarbon field operators to select the best locations for infill drilling to optimize well placement. But what happens when we face a mature tight field which has hundreds or even thousands of developing wells? Usually, it is not uncommon for a company to have hundreds or thousands of infill candidates to choose from in the tight hydrocarbon fields.
Abstract The subject field is a highly heterogeneous giant offshore reservoir. Current field development is predicated upon line drive water injection with 1 km spacing; however, it is anticipated that some oil will be bypassed due to geologic heterogeneity. In order to address the bypassed oil and improve recovery, a simulation study evaluating infill well potential for the target reservoir and an optimization of the full field development plan with infills was carried out. This reservoir consists of two geologically similar areas which are a "Homogeneous" area and a "Heterogeneous" area. High permeability streaks (HKS) having ten times higher permeability than the matrix permeability are dominant in the Heterogeneous area while HKS are significantly less prevalent in the Homogeneous area. Two sector models which represent the Heterogeneous and the Homogeneous areas were generated and sensitivity simulations were carried out to evaluate the vertical and lateral placement of infills. Based on sector model findings, full field simulations were carried out to generate an optimized full field development plan with infills. As a result of sector model simulation for the Heterogeneous area, infill wells showed higher recovery relative to the "No Infill" base case. Vertical and lateral well placement on infill location had little impact on the oil recovery. This is because the HKS in the upper layers were water-saturated by historical water injection from the base 1 km development; hence, water breakthrough at infill wells occurred from HKS within a short period of time wherever infills were drilled. For the Homogeneous area, infill wells showed slightly higher recovery but no oil plateau extension and high water production relative to the "No Infill" base case. Based on these findings it was concluded that (i) infills were required for Heterogeneous area and (ii) infill are not recommended for the Homogeneous area. For the full field evaluation, three different infill scenarios (i.e. 500m spacing infill implementation, 375m spacing infill implementation and no-infill implementation) were evaluated. The optimal infill development scheme for each pattern was chosen by comparing the production performance of each pattern of these three simulations. As a result, in the optimized infill case, infill wells were required primarily in the Heterogeneous area and were not required for the Homogeneous area. Through this analysis, the impact of geological heterogeneity on the performance of infill wells and incremental oil recovery was assessed and the full field development plan was significantly improved. Based on these findings the resulting full-field development plan (i) minimizes the number of infill wells required, (ii) optimizes incremental oil production by addressing the bypassed oil.