Abstract
The drilling and placement of Maximum Reservoir Contact (MRC) wells can be challenging in areas where there is scarcity of available data and/or poor correlation between offset wells. This is especially true for reservoirs with complex geological structural setup, where formation dips may vary significantly within the same lateral drain. Logging while drilling sensors are located away from the bit, which introduces delay and potential errors in evaluating the current bit position. To achieve the well objectives, proactive approach is necessary.
Prior to geosteering the forward modeling is conducted based on geological data, using the expected targets, and accounting for the potential uncertainties such as tectonic environments, target thickness variations, thin target layers, and formation lithology variations. The expected trajectory for MRC may feature dog leg severity limitations to assure successful completion placement, so the drilling Bottom Hole Assembly (BHA) design limitations must be carefully evaluated. To address the complexity of the project it is recommended to place the most important sensors as close to the bit as possible.
The study discusses four wells drilled and completed in the Middle East and covering up to 9,000ft of the drain completed in one run. The major objectives were to land the well as per the provided targets and to stay away within pre-assigned limits such as water level stand-off, etc. For most of the cases, the density, acoustic or resistivity image were the primary mapping means for cases with sufficient contrast allowing to keep the trajectory within the porous target. The near-bit Gamma Ray (GR) with the azimuthal image was used for early reaction to the lithological variations and correlation for the stratigraphic position determination. The rate of penetration and weight on the bit coefficient were used as the earliest indicators for the soft-to-dense transition in contrasting formations. The results allows the revision of the pre-defined Limited Entry Linear (LEL) placements with allocated spacing targeting the highest productivity.
The case study presents various tools and methods that when combined allow to improve wellbore structure and maximize the reservoir targets contact. The use of a pre-job forward model and real-time stratigraphic feature identification using a fit-for-purpose bottom hole assembly allows for the accurate placement of the drain and avoidance of missing targets. The results from Logging While Drilling (LWD) allows the confident well completion as per targets while maximizing the production from MRC wells.
