oa Production from Najmah-Sargelu Reservoirs: A formation damage perspective

Unconventional oil reserves occur in the Gotnia Basin, where the Jurassic Najmah, Sargelu and Marrat reservoirs are the main producing targets. The Najmah and Sargelu are predominantly carbonate formations, which have low matrix porosity and permeability; production from these reservoirs relies mainly on fractures. During drilling, the pore matrix and fractures (including hairline and microfractures) can be invaded by filtrates and mud solids, and the presence of shale exacerbates the problem. In this situation, the selection of an appropriate drilling fluid is crucial. In the production phase, the damage to flow channels is usually due to the migration of fine particles, particularly after stimulation, and the damage may occur because of the accumulation of invaded particles<br>in the near-wellbore area due to increased flow rates. The Najmah and Sargelu are proven reservoirs in many fields in northern Kuwait. Production in these fields was assisted by high fracture density and high API gravity. In some fields in northern Kuwait, production from these reservoirs was below expectations, which is attributed to the poor fracturing network. Hydraulic fracturing is the conventional way to improve the production in such wells. Nonetheless, the poor fracturing network will render the induced fractures less prolific due to slow recharge. For the full exploitation of these reservoirs, it is vital to have good rock characterization, including rock mineralogy, formation wettability, pore size and porethroat size distribution. This will assist in selecting the<br>optimal drilling and stimulation fluids. Moreover, the application of best-drilling practices, in combination with the selection of the appropriate perforation techniques, perforation density and length will help in maximizing production from these deep, high-temperature/highpressure reservoirs. To increase the production from low-producing wells, suitable stimulation methods, (like fracture acidizing or proppant fracturing) can be adopted in a procedural manner. A detailed laboratory study, using reservoir cores with the consideration of geomechanical and mineralogical aspects, is crucial to create conductive and stable fractures.