Abstract: Geochemical Analysis of Reservoir Continuity and Connectivity, Arab-D and Hanifa Reservoirs, Abqaiq Field, Saudi Arabia

Mahdi Abu Ali, George Grover, Rong Hwang, David Baskin

Organic geochemistry and its integration with geologic and reservoir engineering data is becoming increasingly utilized to assist geologists and petroleum engineers in solving production related problems. In Abqaiq Field of eastern Saudi Arabia, gas chromatographic analysis (FSCOT) of produced oils from the Arab-D and Hanifa reservoirs was used to evaluate vertical and lateral continuity within and between these reservoirs. Bulk and molecular properties of produced Arab-D oils do not vary significantly over the 70 km length and 10 km width of the reservoir. Hanifa oils, however, do reflect two compositionally distinct populations that are not in lateral communication, compatible with the occurrence of a large oil pool in the southern part of the field, and a separate, and smaller northern accumulation. The Arab-D and underlying Hanifa oil pools are separated by over 450' of impermeable carbonates of the Jubaila Formation, yet the southern Hanifa pool and the Arab-D have been in pressure communication since onset of Hanifa production in 1954. Recent borehole imaging and core data from horizontal Hanifa wells confirmed the long suspected occurrence of fractures responsible for fluid transmissibility within the porous (up to 35%) but tight (<10md matrix K) Hanifa reservoir, and between the Hanifa and Arab-D. The nearly identical hydrocarbon composition of oils from the Arab-D and southern Hanifa pool provided the final confirmation of fluid communication between the two reservoirs, and extension of a Hanifa fracture-fault network via the Jubaila Formation This work lead to acquisition of 3-D seismic to image and map the fracture-fault system. The molecular fingerprinting approach demonstrated that produced oils can be used to evaluate vertical and lateral reservoir continuity, and at Abqaiq Field confirmed, in part, the need to produce the Hanifa reservoir via horizontal wells to arrest the reservoir communication that occurs with existing vertical wells.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France