In 2010, Petrolera Indovenezolana S.A. (PIV), a joint venture between Corporación Venezolana del Petróleo (CVP) and the Indian company ONGC Videsh Limited (OVL), started planning for two horizontal wells in the Norte Zuata (San Cristóbal) field in the Orinoco belt of eastern Venezuela. The focus for this campaign was to evaluate the productivity of horizontal wells in thin sands and avoid areas of complex geology because of the high uncertainty in the structural behavior, applying technology that provided absolute control of the drilling process into the Oficina formation. Within the Oficina formation, thin sand reservoirs with variations in thickness and dip, geologically facies changes and subseismic faults presented the main challenge to geosteering a horizontal well. Because the project faced high geological uncertainties, a pilot hole was drilled as the first stage in the first well to verify the structural levels and the continuity of the sand bodies. To achieve the above challenges, the combination of a rotary steerable system (RSS) "point-the-bit" and a deep azimuthal electromagnetic resistivity tool (DAEMR) was used. The measurements provided accurate information to the well-placement engineers for proactive decisions in real time, mitigating the possible loss of the target by these geologic uncertainties. High-quality and valuable data for real time geological model update were the expected results obtained from the effort made by PIV in the Norte Zuata (San Cristóbal) field, and the data showed the oil-producing potential of one of the main reservoir (Sand F, G). This application of high-tier technologies demonstrated that drilling and data measurements can be improved and optimized to yield added value for reservoir development and 100% net to gross (NTG) targets. This reduces operational cost, makes it possible to drill in the right place the first time, and pushes forward the limit of the achievable in terms of reservoir exposure.
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 ЉH SandЉ 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 ЉH SandЉ 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.
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