Tectonic Evolution of the Jurassic Humma Marrat Structure, Kuwait and Saudi Arabia Partitioned Neutral (Divided) Zone

Osama A. Al-Shaarawy*, Abdulaziz Al-Najim, Mohamed Rajab, and Eisa Gholoum
Joint Operations Group, KOC and Saudi Arabian Texaco
*[email protected]

The Humma structure is an elongated, NNW-oriented, doubly plunging anticline situated in the southwestern corner of the Partitioned Neutral (Divided) Zone (PNZ) between Kuwait and Saudi Arabia. It produces from the Jurassic Marrat reservoirs and is the only Jurassic producer in the PNZ. It was discovered in 1998 following several unsuccessful wells that targeted Cretaceous reservoirs beginning in the 1950s. Data from open-hole logs (formation imaging tools, magnetic resonance elemental capture spectroscopy, shear sonic, and Stonely permeability) have been integrated with both the oriented core data and 3-D seismic interpretation to reveal the stratigraphic genesis and the tectonic evolution of the Humma structure. The complexity of the Jurassic Marrat reservoirs is attributed to the rapid change in facies from north to south, as well as from base to top. Depositional environments for the Lower Marrat are predominantly low-energy inner-shelf (inner ramp to lagoonal) settings. The Lower Marrat reservoirs possess a combination of inter-crystalline and moldic porosity with tectonic fracture to breccia porosity. The Middle Marrat reservoirs are a stacked succession of individual and overall shallowing upward cycles. Deposition was in a protected sub-tidal, open shelf lagoon to largely filled intra-shelf basin as part of a progradational parasequence set. Open fractures of massive dolomite matrix characterize the Middle Marrat reservoirs.

Both kinematic and dynamic analyses for the Humma structure revealed that the NNW-trending structural axis for the Humma closure is in-parallel with the major fault that bounds the structure. The NE-SW to NW-SE oriented open fractures are the manifestation of a dextral strike-slip wrench tectonic system as depicted by a simple shear tectonic model. The tectonic evolution of the Humma structure was initiated in the Late Jurassic (Kimmeridgian), culminated during the Early Cretaceous and continued throughout the Late Cretaceous. The simple-shear tectonic model applied to the Humma field is well-expressed by a flower structure associated with both the Jurassic Marrat and Cretaceous Thammama Group. The expression is also interpreted from 3-D seismic of the Shu’aiba Formation, oriented core and borehole image data. The tectonic model applied herein is believed to be applicable elsewhere in the Gulf region. The data integration, assimilation and analysis approach, proposed in this presentation, is recommended for similar complex reservoir studies in other parts of the Gulf region.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain