Conventional hydraulic fracturing has been widely used to improve production within low permeability formations for the past 50 years. However, it is not as widely known for improving production within more moderate permeability formations. This paper pertains to the use of hydraulic fracturing in one such formation, the Pinda Sandstone, within the North N’Dola field, offshore Angola.
Hydraulic fracturing within this field was optimized utilizing advances in fracturing treatment technology for these deviated wells. These advances include using various point-source perforating schemes and proppant slugs to mitigate the creation of multiple fractures and near wellbore friction problems. These perforating schemes are compared as to length of perforated interval, shot phasing, number of shots per foot, and gun diameter. Also, proppant slug sizes and concentrations are discussed as to relative benefits in mitigating near wellbore problems associated with fracturing of deviated wells. Real-time data acquisition and analysis, including step-down testing, were included as part of the optimization process. Thirteen of the 15 fracturing treatments incorporated a live annulus for pressure monitoring purposes. Minifracs were utilized on every fracturing interval as a combination fluid efficiency test, fracturing model confirmation, and to carry the proppant slugs. Computer processed, stress logs were successfully used as an aid in selecting intervals with lower fracture initiation pressures. A continuously mixed, high-temperature, borate crosslinked, fracturing gel made from seawater was successfully employed. Also, a high temperature, encapsulated scale inhibitor was also used to control scaling problems that have plagued offsetting fields.
Production clean up procedures are discussed including the production ramp up procedures to mitigate proppant flow back, and the use of a hydrocylone desanding unit for proppant removal at the surface. This paper will also discuss the logistical challenges that this project created including the use of skid mounted, fracturing equipment and materials offshore aboard a tender rig.