Applied Borehole Image Analysis in Complex Sedimentological and Structural Settings: A Single Well Case Study, California, USA
- Aimen Amer (Schlumberger Tech Services) | Michael Raymond Glascock | Jon R. Schwalbach (Aera Enegry LLC) | Masood Khan (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 30 October-2 November, Denver, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.6.1 Open hole/cased hole log analysis, 2.4.3 Sand/Solids Control, 1.2.3 Rock properties, 1.6.9 Coring, Fishing, 4.3.4 Scale, 5.1 Reservoir Characterisation, 1.6 Drilling Operations, 5.1.2 Faults and Fracture Characterisation, 5.8.2 Shale Gas, 5.1.5 Geologic Modeling, 3.3.2 Borehole Imaging and Wellbore Seismic, 5.1.3 Sedimentology, 4.1.5 Processing Equipment, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc)
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Borehole images are typically used to obtain the structural dip of the formations penetrated by a well, identify thinly bedded reservoirs, and analyze fractures and faults (especially those of subseismic scale). In this paper borehole images are used as depositional environment interpretation tools to identify different elements of a deepwater system and to correlate features observed on borehole images to those exposed at outcrops that are analogs for these deposits. In addition, borehole images are used to verify structural interpretation near the well, which is particularly valuable in areas with poor quality seismic data.
The borehole images captured from a single well in the Ventura basin, California, contain excellent examples of sedimentary features such as groove casts, lenticular bedding, scours, graded beds, and. rip-up clasts. These features enable us to interpret depositional facies such as debris flows, channels, and amalgamated and layered turbidites to better understand the position of the well within the depositional system. We are also able to identify and verify overturned beds and repeat stratigraphic sections in the well because the image logs enable us to document the presence of reverse faults. The outcrop analogs we discuss are from the Pliocene Pico formation from the Ventura basin in California. Features observed on the outcrops are similar to features observed on borehole images and in cores, allowing us to extend our facies interpretation to larger areas of the field.
Detailed structural analysis of the image log from this well using manually-interpreted formation dips shows three large-scale thrust zones (at least 3000 ft each) associated with highly tilted and in one case overturned beds. This analysis enhanced our structural understanding of this compressional regime. This is an important tool in areas such as the Ventura basin, where seismic data is not easily acquired because of the rugged terrain and steeply dipping structural limbs.
Combining the sedimentological and structural information from the borehole image interpretation provides a better understanding of the reservoir geometry and likely connectivity between reservoir units. This information is critical for choosing the next well location and planning future development strategy. This paper demonstrates the value of utilizing borehole images to understand local depositional systems and complex structures within an active field development program.
The Ventura Avenue field is in the central part of the Ventura-Santa Barbara basin in California. The basin is a prolific hydrocarbon system, with both onshore (Ventura basin) and offshore (Santa Barbara basin) portions containing major oil fields (Galloway 2006). Ventura Avenue field has produced more than a billion barrels of oil during its century plus history of exploration and production. The borehole images reviewed in this paper were obtained from a well in the field drilled and logged in 2008.
Fig.1 (after Schwartz et al. 2007) illustrates the location of Ventura Avenue field, and depicts the generalized depositional system interpreted during the Pliocene. The east-west trending depositional trough was supplied with abundant clastic sediments sourced primarily from the east (Hsu et al. 1980). In the Ventura field area, the depositional units are interpreted as a series of offlapping, compensationally stacked fan lobes, fed by distributary channels. The basin is topographically confined by basin-bounding thrust faults: the San Cayetono system to the north, and the Oak Ridge system to the south (Yeats 1976).
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