Geosteering Horizontal Wells to Maximize Oil Recovery in the Mid Cretaceous Shuaiba Fm. Oman

John P. Watkins and Abdullah Hamdi
Petroleum Development Oman, Muscat, Oman

Petroleum development Oman has been using Geosteered horizontal wells in the Qarn Alam area to maximize the oil recovery rates, production, and minimize attic oil. The Shuaiba Fm. is a mid Cretaceous carbonate platform in this area, with a four million year old erosion surface. To complicate matters, the Shuaiba is also faulted, fractured and has erosional channels cut across this surface. The mid Cretaceous Nahr Umr shale conformably overlies the Shuaiba and provides the seal for the reservoir. The resistivity, acoustic, and seismic characteristics of the Shuaiba carbonate and the Nahr Umr shale are unfortunately very similar (example low resistivities of 1 to 4 Ohms for the Shuaiba reservoir and 0.6 to 1 Ohm for the Nahr Umr shale). The objective of Geosteering is to stay within a zone 1.5 meters from the Shuaiba/Nahr Umr interface (Shuaiba erosional surface) where the Shuaiba reservoir characteristics are optimum without exiting into the overlying Shale. Staying in this zone results in an increase in production and NPV. Exits are costly in drilling, deferred oil, and hardware. Resistivity response (deep phase and deep attenuation) is the main Geosteering tool used Gamma Ray and ROP also being important. Currently this technique has been tried in 3 fields in Qarn Alam using different contractors and LWD tools. Geosteering has resulted in wells being drilled within the 1.5 meter target more than 80% of the time, with exits into the overlying shale being cut to less than 0.8 exits per 2km of hole drilled.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece