This paper describes the combination of strategies deployed to optimize horizontal well placement in a 40 ft thick isotropic sand with very low resistivity contrast compared to an underlying anisotropic shale in Semoga field. These strategies were developed due to previously unsuccessful attempts to drill a horizontal well with multiple side-tracks that was finally drilled and completed as a high-inclined well. To maximize reservoir contact of the subject horizontal well, a new methodology on well placement was developed by applying lessons learned, taking into account the additional challenges within this well. The first approach was to conduct a thorough analysis on the previous inclined well to evaluate each formation layer’s anisotropy ratio to be used in an effective geosteering model that could better simulate the real time environment. Correct selections of geosteering tools based on comprehensive pre-well modelling was considered to ensure on-target landing section to facilitate an effective lateral section. A comprehensive geosteering pre-well model was constructed to guide real-time operations. In the subject horizontal well, landing strategy was analysed in four stages of anisotropy ratio. The lateral section strategy focused on how to cater for the expected fault and maintain the trajectory to maximize reservoir exposure. Execution of the geosteering operations resulted in 100% reservoir contact. By monitoring the behaviour of shale anisotropy ratio from resistivity measurements and gamma ray at-bit data while drilling, the subject well was precisely landed at 11.5 ft TVD below the top of target sand. In the lateral section, wellbore trajectory intersected two faults exhibiting greater associated throw compared to the seismic estimate. Resistivity geo-signal and azimuthal resistivity responses were used to maintain the wellbore attitude inside the target reservoir. In this case history well with a low resistivity contrast environment, this methodology successfully enabled efficient operations to land the well precisely at the target with minimum borehole tortuosity. This was achieved by reducing geological uncertainty due to anomalous resistivity data responding to shale electrical anisotropy. Recognition of these electromagnetic resistivity values also played an important role in identifying the overlain anisotropic shale layer, hence avoiding reservoir exit. This workflow also helped in benchmarking future horizontal well placement operations in Semoga Field. Technical Categories: Geosteering and Well Placement, Reservoir Engineering, Low resistivity Low Contrast Reservoir Evaluation, Real-Time Operations, Case Studies

The geothermal drilling environment presents many obstacles that limit the use of directional-drilling and logging-while-drilling (LWD) technologies, such as borehole washout, mud losses, severe vibration, and high temperature. The case study presented in this paper demonstrates a novel practice to enhance data logging in geothermal drilling by deploying advanced telemetry and LWD technologies. This operation aims for continuous improvement in geothermal drilling operations. The case study covers the 12.25-in. hole section of well XXE-05 in the Sorik Marapi Geothermal Field. The LWD string consisted of electromagnetic (EM) telemetry, pressure while drilling (PWD), vibration (DDSr), and acoustic caliper (ACAL). Through this tool configuration, the operator acquired drilling mechanics and caliper logs in real-time and recorded mode, enabling effective monitoring and evaluation of wellbore stability. Throughout the real-time acquisition, EM telemetry provided a data rate to the surface unit three times faster than conventional tools. Furthermore, with the integration of caliper and drilling mechanics data (vibration and equivalent circulating density), the borehole conditions became more visible to the directional driller, allowing better control of drilling parameters to minimize vibration and achieve optimum hole cleaning in washed-out or tight formation sequences. The recorded data from the caliper sensor indicated an average of 8.6% washout for the entire 12.25-in. interval. Washout intervals were compared with loss occurrence during drilling and the presence of smectite-bearing paleosols, showing that the washout zones associate with the latter, supporting the smectite-bearing paleosol model in explaining the cause of stuck pipe incidents in the Sorik Marapi field. In addition, measurements of hole ovality were compared with the interpreted fault trend, providing further insight into the existing model. In general, this LWD case study has given added value through geothermal borehole characterization, from drilling hazard identification to subsurface analysis. Identified challenges while running LWD in this geothermal environment were addressed for future improvements, such as the effect of tool eccentricity and the impact of vibration. Perusal of both real-time and recorded caliper and drilling-mechanics data has opened various possibilities for maximizing the sensor usage in future wells.

The main challenge in offshore Southeast Sumatra, as one of Indonesia's mature fields, is to increase production in existing assets. The approach taken by the operator is through side-track drilling from historical wells, planned as a series of infill development wells, whilst evaluating new potential plays. This case study examines the logging-while-drilling (LWD) data acquisition in the Krisna-XX well in the Krisna field, which was designed to drain the remaining reserves from the Lower Baturaja limestone formation in the Sunda basin and maximize undrained area oil potential. Based on simulation analysis, the estimated reserves in the Lower Baturaja were 581 MBO with an initial rate of 426 BOPD. Additionally, the completion strategy required a rat hole to be drilled into the basement, which elsewhere in the basin can be hydrocarbon bearing. The first two wells drilled in the Krisna Field experienced severe mud losses while drilling, which had caused significant invisible non-productive time (NPT). The losses were associated with potential natural fracture swarms in the limestones and basement formations, but the fracture apertures were below the resolution of the LWD density image tool used in those wells. Hence, to refine evaluation of the fractures, an azimuthally focused resistivity tool was utilized in the third well (Krisna-XX), providing omni-directional laterolog resistivity and high-resolution resistivity images. The high-resolution resistivity tool was run in combination with quad-combo LWD tools to drill and log the high-angle (>70° inclination) 8.5-in. reservoir section. While drilling both the reservoir and basement intervals, this well also experienced high dynamic loss rates of water-based drilling fluids, which were treated with a lost circulation material, minimizing impact on the reservoir productivity. The well was drilled to total depth (TD) without incident. The aim was to utilize borehole imaging memory data acquired from this section as a benchmark for examining the current state of the Sunda Basin's formation. Post-run analysis of the memory image data yielded excellent quality high-definition images over the interval of the carbonate reservoir, coal, claystone, and basement sequences, improving knowledge of the Sunda Basin's detailed geological structure. This result helped the operator to understand the reservoir facies characterization of the Lower Baturaja formation, while overcoming potential fluid-loss conditions of up to 250-300 bbl/hr. The images clearly showed sedimentary structures, natural fracture networks, drilling induced fractures and vugs. Subsequently, by comparing against actual production (which has reached up to 1,842 BOPD), analysis of weak zones will improve reservoir insight to be incorporated into future subsurface models. In addition, high-resolution images combined with pressure-while-drilling data complements drilling operations analysis. Correlation to the intervals of fluid loss has allowed the operator to improve time and cost efficiency of the drilling operation and forthcoming planning.

The Kutai Basin, has been under production for more than 40 years and many wells have been drilled to develop the area. This has resulted in reservoir-induced drilling problems, like kicks and lost circulation due to depletion, while some high-pressure zones still exist. This complexity makes pore-pressure and stress analysis difficult. To address this problem, a comprehensive reservoir-evaluation program was developed by adding formation pressure testing to the planned quad-combo logging-while-drilling (LWD) program. Pressure measurements in this development stage were planned to aid the operator's understanding of the field's current hydraulic communication pathways, to relate reservoir characterization to the geological model. Emphasis was on the insight of static reservoir pressures, which are important for confirming fluid contacts and fluid density gradients. Methods of formation pressure testing have evolved over many years. Through this paper's case study, recent LWD and wireline pressure-testing technology are elaborated in depth, in relation to two sequential wells drilled offshore in the Kutai Basin. LWD pressure-testing operations were conducted in well XX-5 in a dedicated run after completion of drilling the section. The wireline test was conducted in well XX-4 as an open-hole logging run, along with the acquisition of fluid analysis data. Both systems were successfully utilized in the 6-inch hole sections of the subject wells, in a depleted reservoir, with the pressure overbalance expected to reach around 3100 psi in the pre-job planning stage. The average mobility was low in both sets of pressure test results, as also align with the reservoir's current depletion state. Challenges related to tight tests and lost seals in this mature field were experienced with both systems. The drilling environment and the formation's exposure conditions may have presented varying challenges; nevertheless, the same relatable quality has been achieved with both types of testing (LWD and wireline). This paper describes in detail the planning, design, and performance of pressure testing using LWD and wireline in the Kutai Basin. Comparisons between results are displayed to highlight the current character of the subject offshore field. This study aims to enhance future drilling and logging operations, by reviewing solutions from formation pressure testing technologies and to add value to mature and depleted field planning. Technical Categories: Geotechnical, Geoscience & Geophysics; Drilling Technology