Real Time Reservoir Mapping While Drilling Reduces Risks, Geological and Fluid Position Uncertainty in the Gulf of Mexico

Abstract

Abstract Reservoirs in the Northern Gulf of Mexico (NGOM) are predominantly drilled with low angle wells. Drilling a well horizontally presents its own set of challenges. The Mississippi Canyon block 22/21 operated by ANKOR Energy embodies the significant drilling challenges sometimes found in the NGOM reservoirs. The "H Sand" reservoir is a low resistivity (3 to 5 ohm.m) reservoir bounded by a northeast southwest fault. The overburden is uniform for more than 200ft TVD above the reservoir, making the landing challenging with conventional well placement techniques. The operator was planning a 2200ft lateral section to be drilled close to the Gas Oil Contact (GOC). Early water production was observed in the offset well located at the toe of the planned well, questioning the current position of the Oil Water Contact (OWC). Landing this well is challenging from both a geological and drilling point of view as a 3D trajectory is required to avoid the fault and offset wells. In light of these challenges, the operator decided to use the very-deep electromagnetic (EM) directional resistivity tool with its detection range of more than 100ft, enabling the detection of the top of the H sand reservoir long before landing. In the lateral section, the tool was used in conjunction with an integrated petrophysical platform to map the top of the reservoir, detect the OWC and identify the lithology and fluids present while drilling. While landing the well, the top of the H sand reservoir was detected 48ft TVD away – 10ft deeper than expected. The very-deep directional resistivity tool enabled the well to be confidently landed despite the lack of correlation markers and depth uncertainty of the "H Sand" reservoir. The OWC was detected more than 70ft below the well during the landing section even though the bit had not penetrated the H sand reservoir yet. The top of the reservoir and the OWC were mapped throughout the length of the lateral section along with the lithology and fluid content. Towards the toe of the lateral section, near a producing offset well, the OWC, still 50ft below the current trajectory, was observed to be rising up and getting closer to the well. Total Depth (TD) was called early to avoid premature water production. Water coning was confirmed as the reason behind early water production in the offset well. The use of this technology during the landing and the lateral section of the well reduced dramatically the risk associated with geological uncertainty as well as fluid contact position providing critical information for field management planning.