ABSTRACT
Pore volume compressibilities have a major impact on recovery estimates for unconsolidated sand reservoirs. A realistic estimate of the recovery factors is imperative to prospect development decisions. Confirmation of higher pore volume compressibilities may lead to development of new discoveries or preclude secondary recovery measures in complicated reservoir systems. By performing a pulse test at the East Breaks 165 field, an "in situ" measurement of pore volume compressibility for a producing Gulf of Mexico unconsolidated reservoir was obtained to verify the large compressibilities measured from uniaxial core testing.
The pulse test was run between two East Breaks 16S wells. High quality pressure data was obtained, and the formation’s diffusivity and transmissivity were determined. To extract the formation’s pore volume compressibility from the test data, key components of the reservoir had to be suitably identified. PVT work was required to confirm that the reservoir was not originally at its bubble-point as first assumed, and therefore, no free gas was present in the system to mask the pore volume compressibility. In addition, the approximated reservoir thickness produced an unrealistic estimate of pore volume compressibility. Consequently, a production log was run in the puiser well indicating that two-thirds of the perforated interval was not contributing to flow. Utilizing this additional information, the final pore volume compressibility derived from the pulse test compared favorably with the core data.
An outgrowth of this investigation was a better understanding of the suspected formation damage believed to be caused by fines migration. Interpretation of the related pressure build-ups reflected extremely high damage in both welk. The production log and a subsequent pulse neutron log confirmed the probability of significant fines movement in the formation. These results substantiated the deterioration of well productivity observed over the past three years. Identification of near wellbore damage and its cause will allow appropriate remedial work to recover lost well capacity and maximize reserves recovery.
