Fault and Fracture Characterization Using 3D Interval Pressure Transient Tests

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Abstract Permeability is one of the most important parameters that affects almost all phases of reservoir management and well performance. It is considered to be the most basic formation property and a tensor (directional dependence). As stated well by Weber1 in 1986: "Reservoir heterogeneity is among the major reasons why enhanced oil recovery is so difficult. Projects undertaken without detail reservoir evaluation often end in failures related to unexpected baffles to flow, permeability heterogeneity, or wrong appreciation of the residual oil distribution." Fractures and faults can behave as barriers, baffles, or open channels to fluid flow in the reservoir and often cause early water breakthrough, gas channeling, etc. that are costly. In this paper, we use 3D interval pressure transient tests to estimate horizontal and vertical permeabilities and to delineate of fracture and fault conductivities. 3D interval pressure transient tests are conducted using the wireline conveyed dual-inflatable-packer module with multiple observation probes that can be set along the wellbore a number of times as the number of fracture and fault zones require. The dual-packer, with one meter open interval is set against the borehole wall to hydraulically isolate the tested section from the rest of the wellbore. In this set up, the dual-packer open interval encircles fractured and/or faulted zones. The formation fluid is produced through the isolated packer interval for more than a few hours, after which a pressure buildup test takes place. For the interval tests, the observation probes are usually mounted above and/or below the packer module. These probes measure pressure changes due production from the open interval at different locations in the formation. For the interpretation of each interval test, first we use the well-known flow regime identification methods of pressure transient testing. After the flow regime identification and analysis, we use a computationally efficient optimization algorithm that allows simultaneous nonlinear parameter estimation of the unknown parameters (horizontal and vertical permeabilities and fracture and fault conductivities) from 3D transient pressure measurements that are spatially distributed. For this nonlinear estimation or history matching, a detailed reservoir model is constructed by incorporating to all geological and well openhole log data, particularly resistivity images that are crucial for identifying, testing, and modeling faults and fractures. During the minimization process, the reservoir model and its parameters are updated as all pressure measurements are matched with the model behavior. This process is continued until a satisfactory match is obtained for all 3D transient pressure tests. Two examples (one synthetic and one actual field data) are presented to demonstrate the application of the methodology.