The Great Burgan reservoir is the largest sandstone oilfield in the world, it has been developed and produced since the 1930s. Historically developed through deviated wells, a new project of horizontal wells was initiated recently to produce from the UB3 reservoir unit. A pilot hole is usually required to identify the presence of productive sublayers and the depth of the oil-water contact (OWC), which must be avoided in the horizontal section. Elimination of the pilot hole would help to minimize the time and cost of development (Al Khalifa et al. 2020). The azimuthal ultra-deep resistivity mapping service (UDR) has proven its capability to eliminate the need for pilot holes by mapping reservoir boundaries and OWC on the fly, earlier than with traditional methods. This facilitates real-time geosteering to land the well in a single drilling run in the productive zone. Additionally, it helps to reduce non-productive time by making it easier to stop drilling and set casing above a target layer and to help optimize future well planning in field development. A feasibility study performed on offset wells showed promising potential from application of this method in the UB3. Real-time UDR geomapping detected multiple thin sand lenses on top of UB3 but showed that they were not of commercial capacity. The decision was made to continue drilling deeper for a larger sand layer. The UDR detected a massive sand below the smaller lenses and the well was landed in it. Early mapping also helped to optimize the landing with the desired inclination and dog-leg severity. The OWC was detected ~35 ft TVD below the landing point. Without UDR it would have been impossible to detect the OWC and very challenging to perform an accurate landing. The target could have been missed by landing either too shallow or too deep or with the wrong inclination. Following the landing of the well the lateral section was drilled through upper and lower lobes of the massive sand with a total cut of 1649 ft MD. This comprised 450 ft MD of upper lobe, 350 ft MD of transition interval, and 637 ft MD of lower lobe inside BU3, with an average porosity of 30 p.u. and a water saturation of less than 10%. Formation pressure tests measured mobility of up to ~3.4 D/cp. This case study demonstrates that utilization of the ultra-deep resistivity mapping service enabled a new approach to drilling lateral wells in the Burgan field development, improving reservoir insight and reducing well drilling time and cost.

The mature Greater Burgan field is the largest clastic oil reservoir in the world producing from multiple clastic reservoirs. With growing surface area congestion affecting rig moves, current wells are drilled with high deviation often through unstable overburden shales. Well trajectories are getting more complex, resulting in a large increase in hole instability events associated with stuck pipes, loss of bottom hole assemblies often leading to side-tracks, challenging well logging conditions and well completion operations. This paper discusses a holistic and practical geomechanical approach to solve the instability problems, based on understanding the rock failure mechanism of shale, and also discusses the implementation of an integrated solution to drill, log and complete the wells successfully. A thorough geomechanical analysis was done on several wells. Drilling data analytics helped to understand the relationship among formation instability, well trajectory and mud parameters. Lab tests (chemical and mechanical) were performed to determine the chemical and mechanical behaviour of the rock and its interaction with drilling fluid. Anisotropic shale strength tests were targeted to know the rock strength variation with respect to angle of attack. Geomechanical models were prepared and calibrated with observations of drilling problems. Based on integration of models and experiences, effective solutions were devised to implement at well planning as well as drilling stages. A combination of measured and modelled parameters suggested that multiple failure mechanisms are active to induce shale failure including (a) stress induced borehole breakouts, (b) chemoporoelastic interaction of mud and rock fluid and (c) weakening of shale bedding planes and micro fractures. A customized real-time geomechanical monitoring solution was implemented for improved drilling performance and efficient completion of new wells. Specific mud design and mud weights for drilling high angle wells (65-70 deg) were generated and used in real-time while drilling. With the help of LWD and mud logging data, real-time decisions were taken based on well behaviour to drill the wells in a single casing section. Wireline logging and lowering of completion string was completed without any resistance even after the long section of shale was exposed for several days. This entire re-engineering of the process was accepted as a cost-effective and efficient solution that is being recorded as a best practice for implementation in future wells. Integration of diverse disciplines (geomechanical, geochemical, petrophysical and drilling engineering) was successfully implemented to drill a complex well. Real-time geomechanics along with customized drilling fluid and drilling practices enhanced the drilling efficiency. This integrated solution is expected to significantly reduce non-productive time in future upcoming wells with complex well profiles.