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Resolving Structural Complexities In The Tulare Fold Belt: Implications For Oilfield Development In The South Central Cymric Oilfield, Kern County, California


The Tulare Fold Belt in the southern portion of the Cymric Oilfield is a shallow northeast verging fold and thrust system that largely affects the San Joaquin and Tulare formations. It is known that understanding the complex structural geometries within the thrust system is paramount to effectively developing reserves in the shallow heavy oil reservoirs. Resolving the structural geometries is challenging due to varying structural styles within the fold belt. It is observed that fault geometries in the western portion of the study area are steeply dipping fault propagation folds with very strong asymmetry, whereas fault geometries in the eastern portion of the study area are flatter and have less asymmetry. Additionally, the faulting and resultant compartmentalization is more intense in the west as compared to the eastern area where there may be little to no compartmentalization. Mapping each fault in detail is challenging as each thrust appears to have unique geometry in terms of the vertical and horizontal extent. The varying structural styles across the fold belt can be attributed to: 1.) growth and propagation basinward of the thrust front and, 2.) effects of an older underlying structural feature (1Y Anticline). Detailed mapping of the fault planes and delineation of the structural compartments is important because each compartment contains beds with varying dip magnitude and fluid levels. Understanding the location of each dip domain within the structural compartment is critical as this affects well placement decisions in turn, optimizing hydrocarbon recovery. Adding to the challenge of this problem is the inherent depositional complexity within the stratigraphic units. The active uplift of the 1Y Anticline during deposition of the Etchegoin, San Joaquin, and Tulare formations has resulted in a stratigraphic thinning over the crest of the anticline as well as stratigraphic thickening off structure. The stratigraphically youngest unit, Tulare Formation, was deposited in a progradational fluviodeltaic system. The Tulare Formation is lithologically heterogeneous and comprises many different lithofacies, both horizontally and vertically. Sands within the Tulare Formation are discontinuous and correlation can be difficult between structural compartments. This lithologic discontinuity is a problem when attempting to generate balanced cross sections as the standard methods require an assumption of uniform parallel bedding and concentric folding.