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Abstract Middle East carbonates frequently are heterogeneous in nature, encompassing variable pore types, strong diagenetic overprints, variable wettability and fracture networks amongst other effects. Resistivity borehole images have long been an integral constituent to understanding their complexity and unlocking volumes. High resolution LWD resistivity images were first introduced in the 1990's, however as downhole environments became progressively more challenging, resistivity images suffered from the dynamic acquisition environment resulting in severely degraded images. The Al Shaheen field has been developed with Extended Reach Drilling (ERD) wells, and wells of 30,000 feet are commonplace. Early LWD resistivity image data suffered from excessive stick and slip, with approximately half of the wellbore suffering from poor quality image data, degrading with depth. The outer portion of the wellbore is prohibitive to impossible to access via conventional drill pipe conveyed tools, resulting in an absolute requirement for high quality LWD resistivity images. The new methodology redefines the acquisition and processing methodology, resulting in images unaffected by stick slip with a 100% success rate in the most challenging of ERD environments. This paper illustrates the improvements in logging while drilling images (LWD) and subsequent fracture network characterization as a result of implementing a new image acquisition strategy and processing algorithm. The paper explores the close collaboration necessary to drive the innovation to dramatically enhance existing technology, and demonstrates the results with comparisons of the LWD images using the old and new methodologies. The development of the Al Shaheen Field The Al Shaheen field was discovered in the 1970's in connection with appraisal drilling of the underlying North Field Khuff reservoir. It is located on the central axis of the Qatar Arch some 70 Kms N-E of the Qatar peninsula, and covers an area of approximately 2080 km2, Figure 1. The reservoirs were initially considered uneconomical due to their thin oil columns. In 1992 Qatar Petroleum entered into an Exploration and Production Sharing agreement with Maersk Oil Qatar and the Al Shaheen field has since been under development, (Thomasen et al, IPTC-10854). The field contains multiple stacked reservoirs, and the main producing targets are the Cretaceous Kharaib B and Shuaiba carbonate formations and the Nahr Umr sandstone formation, Figure 1. The field is being developed using extended reach horizontal wells (ERD), and is home to some of the longest wells in the industry. The application of ERD technology has enabled the large areal accumulation to be developed using only nine production platforms. Horizontal well technology is particularly attractive due to thin producing columns. The length of these horizontal wells has increased over time, pushing the limits of available technology to today where for example wells of 30,000 feet to 40,000 feet are geosteered within a 10-foot window (Sonowal etc al, SPE/IADC-119506). Increases in well lengths also require continuous improvement in associated well technologies from completion technology (Brink et al, SPE-134934), to new logging technology. |
