TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPetroleum well performance and its evaluation are clearly some of the most important functions of modern production engineering. We present a general approach to the issue by employing the field-derived, dimensionless productivity index (J D ) which we calculate from measured information including the production rate, reservoir and flowing pressures and well and reservoir data.The dimensionless J D is independent of well completion, i.e., it transcends the geometry, whether the well is under radial flow, hydraulically fractured or whether it is vertical or horizontal. The determined J D 's are then compared against benchmarks we have developed for optimized production such as the concept of Unified Fracture Design (UFD) or maximized horizontal well performance. We have developed deterministic methods for this analysis and new means to graphically depict the results.Such evaluations are important in concluding whether the well is underperforming or whether the past engineering could have been improved and by how much. Decisions such as refracturing, the redesign and improvement of future treatments and whether to fracture vertical or drill horizontal wells can be readily made.
Refracturing in a plane normal to that of the initial fracture can be beneficial in tight gas fields, even when the initial fracture is deeply penetrating and highly conductive. The magnitude of the benefits will depend on the timing and the penetration of the secondary fracture. The Gas Research Institute has sponsored a project that addresses the conditions required for maximum benefit and the validation of the process with a field trial. This paper addresses the theory and conditions required for maximum benefit. P. 17
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRefracturing can be used to increase production in poorly fractured wells. A different application of this technology is to refracture wells with strong initial fractures. In this paper, we provide evidence of increased production due to refracturing two tight gas wells having deeply penetrating initial fractures. Surface tiltmeter measurements show refracture orientations at oblique angles to the azimuth of the initial fractures.
Hydraulic fracturing has emerged as the compelling completion and stimulation procedure in Russian petroleum production credited to a large extent for the impressive production enhancement experienced in the last several years. We present in this paper approximately one thousand hydraulic fracturing jobs from Western Siberia and their performance is analyzed and compared with design and execution variables. The well performance is measured through, among other things, the actual, field-derived, dimensionless productivity index (JD) and is compared against our concept of Unified Fracture Design (UFD) which has been used to physically optimize and maximize the productivity index from a hydraulic fracture treatment. We have demonstrated in the past that for a given mass of proppant there is a specific dimensionless fracture conductivity, which we called the optimum, at which the JD becomes maximum. The Proppant Number is a seminal quantity unifying the propped fracture and the drainage volumes and the two permeabilities, those of the proppant pack and the reservoir. One of the important observations of our analysis is that the distributions of the achieved JD follow the theoretical curves, however there is a gap between the theoretically achievable and actually achieved JD. We evaluated the gap and identified measures to improve our fracture designs. Conventional fracture designs can be extended considerably by injecting large proppant masses with far better proppant-pack permeabilities within reasonable field and logistical constraints. It is against these two concepts, the desired optimum fracture conductivity for the injected fracture size, and the would-be "pushing the limits," design that we compare the already executed treatments. We provide critique and offer suggestions for design improvements. Introduction We have shown in earlier papers (Demarchos et al., 2004, Economides et al., 2004) that the first gap, the one between the designed (target) JD and the theoretically achievable JD can be closed by selecting higher conductivity proppants, larger proppant volumes and by utilizing UFD to physically optimize the new fracture treatments.This process is already underway in the reservoirs which include the wells studied in this paper. The second gap, the one between the designed JD and the achieved JD is a different story.In order to physically optimize the fracture design and at the same time close the gap between design and execution, some data are extremely important.It is critical to know the reservoir permeability.Given a proppant mass and a proppant volume, the fracture geometry for a reservoir with a permeability of 1 md will differ significantly with the geometry for a reservoir with a permeability of 5 md let alone 15 md.Equally important is the fracture height, because this determines what fraction of the total proppant volume will actually be in the reservoir and contribute to the productivity of the well.Also, the reservoir drainage, allocated to a well is crucial because in each design, the proppant mass is distributed in length and width and the reservoir drainage plays a major role on the proppant number and hence the optimum fracture geometry. The achieved (actual) JD is calculated from production information.In performing this analysis we have discovered that until 2004, the simulated fracture geometry would be taken as true and the reservoir permeability would be adjusted to reflect it.In 2004, this practice was changed appropriately and now the fracture performance is measured using independently derived permeability values and/or fracture geometry, based on fracturing pressure match.
Petroleum-well performance and its evaluation are clearly some of the most important functions of modern production engineering. We present a general approach to the issue by employing the field-derived, dimensionless productivity index (J D ), which we calculate from measured information including the production rate, reservoir and flowing pressures, and well and reservoir data.The J D is independent of well completion (i.e., it transcends the geometry), whether the well is under radial flow, is hydraulically fractured, or whether it is vertical or horizontal. The determined J D s are then compared against benchmarks we have developed for optimized production, such as the concept of unified-fracture design (UFD) or maximized horizontal well performance. We have developed deterministic methods for this analysis and new means to depict the results graphically.Such evaluations are important in concluding whether the well is underperforming or whether past engineering could have been improved and by how much. Decisions such as refracturing, the redesign and improvement of future treatments, and whether to fracture vertical or drill horizontal wells can be readily made.
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