Horizontal drilling is fast becoming an effective economical solution to maximize the asset value for E & P companies. Since established in 2009, TATWEER petroleum is one of those companies that utilize horizontal drilling intensively to improve the production and the recovery factor from tight and fractured carbonate reservoirs within the Bahrain Field. Reservoir complexity and heterogonity create the need for running open-hole logs in most of the horizontal wells within the Bahrain field. Logging is essential for the following: Designing the well completion (Open hole or Slotted liner equipped with external packers), predicting and understanding the well performance, and planning future work-over activities (Water and Gas Shutoff). Normal practice to deploy open hole logging tools into the HZ horizontal section within the Bahrain field was to use drill pipe (Tough Logging Conveyance). Given the typical low productivity of wells, operational costs were of concern. Consequently, TATWEER requested alternative methods to optimize the logging operations in horizontal wells. Of the options offered by Schlumberger, tractoring technology was deemed to be best. The main challenge faced initially was with tractoring in the low uniaxial compressive strength (UCS) of the reservoir formations (UCS=1400-3000 PSI) in Bahrain. Since tractoring is known to be an effective deployment method for hard formations (UCS>5000 PSI), the new OH tractoring technology (UltraTRAC*) was offered by Schlumberger as a solution for this low UCS enviroment. UltraTRAC* was successfully deployed in TATWEER wells, saving 60-70% of the logging time comparing to the normal TLC (Tough Logging Conveyance) operations which represents 5% saving of the total well cost. In this paper, the authors discuss the details of this new logging methodology, logging results, and value obtained from using this technology.

The Awali field is a mature carbonate oil field in Bahrain. It is a giant gentle limb of anticline compartmentalized by numerous normal faults. The reservoir is intersected by normal faults that create half-graben reservoirs. Characterizing these faults through borehole data is necessary to understand the reservoir compartmentalization and improve the geologic model, which was built from seismic data of poor vertical resolution. Fault structure was characterized by the deep directional resistivity of a logging-while-drilling (LWD) tool used to geosteer horizontal wells through faulted zones. The LWD tool detected the faults, determined their throw and estimated its extent, and mapped the bed boundaries up and down within its depth of investigation. With this information, engineers were able to place wells over horizontal sections ranging from 1,000–3,500 ft [305–1,067 m] MD within the target zone and stay just 4–14ft [1.2–4.3 m] below the roof (i.e. the top of the Kharaib carbonate reservoir). The high-resolution wireline borehole image logs recorded after the well reached TD provided further confirmation of fault presence and strike and dip angle. On borehole image logs, normally the faults are indicated by fracture association and drag pattern on nearby structural bedding dips or by abrupt facies or textural changes. Most faults in the Awali field have NW–SE trends with high dip angle; they are considered as a normal fault regime forming the graben and half-graben reservoir traps. Combining the complementary LWD well-placement results and high-resolution borehole image log interpretation enabled us to determine the fault type and its orientation.