Beating the Bit – Using 2-D Structural Cross Sections to Drive Rapid Development of Highly Deformed Monterey in the Elk Hills Field, California

Abstract

The structurally complex, compressive tectonics of the southern San Joaquin Basin, and the fractal scales of highly-deformed strata in the Monterey Formation combine to create a geologic setting challenging to model in three dimensions. This study provides insight into how the interpretation of dip-meter data and construction of two-dimensional balanced cross-sections can drive decisions in a rapid development environment.

In 2008, re-interpretation of dip-meter data from an older vintage well led to the drilling and discovery of the Gunslinger Anticline in the Elk Hills Oil Field of California. In 2009, CRC began development of the Miocene Monterey Formation on the Gunslinger Anticline and by the end of 2011, over 100 wells had been drilled. Evaluating closure along the north flank and down the plunge of the anticline was difficult due to poor quality seismic imaging. Therefore, the primary source of structural information came from drilling new wells. As wells pushed downdip, targets consistently came in “deeper and steeper.” Dip-meter data indicated that the north flank is actually vertical to overturned depending upon on-strike location. Predicting drilling targets became increasingly challenging, but the fast-paced development and complex structure precluded building a 3D model.

Dip-meter data were essential in generating the structural framework, as well as characterizing the deformation and resultant fracture system in the Monterey Formation. All incoming image logs were quickly interpreted for dip and azimuth of both bedding and fractures, as well as fracture type, apertures, and frequency. One of the primary challenges was distinguishing the first-order structural features from the widespread parasitic folding and other pervasive small-scale disruptions.

Several balanced 2D dip-sections were utilized to elucidate the complex deformation history, which allowed for improved fracture modeling and more accurate drilling locations. These 2D sections successfully informed step-out wells up to 1,000 feet from existing well data with no seismic control. Despite the new technology available, what worked best during rapid drilling of this structurally complex area, was a back-to-basics approach that offered a strong reminder that 2D cross-sections are still a powerful tool which can be used to make key business decisions.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018