Horizontal drilling has demonstrated its superiority in developing the Middle Marat reservoir within the Umm Gudair (UG) field in Kuwait. However, achieving precise placement of the lateral section in thin carbonate layers requires meticulous geo-steering. Due to environmental concerns and the high operational costs associated with using radioactive-based porosity logging tools in such wellbore profiles, the preferred method for geo-steering is to utilize Logging-While-Drilling (LWD) gamma ray and resistivity logs (Nguyen et al, 2022). When drilling with a 4 ½″ slim hole, LWD data can suffer from poor quality due to a low signal-to-noise ratio or complete loss of signal caused by mud telemetry issues. To address this challenge, advanced cutting analysis techniques, including X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF), have been integrated with LWD to enhance the accuracy of lateral sidetracking in the UG field.
Advanced analysis performed on cuttings recovered on the surface while drilling confirms that the wellbore remains within the targeted sub-layer, while LWD data monitors larger-scale boundaries. This approach is illustrated in a limestone formation sub-layer with a thickness of approximately 20 feet, characterized by low natural radiation and minimal resistivity contrast with adjacent sub-layers. A thorough pre-job study was conducted using advanced analysis on cuttings from offset wells, with data resolution at 10 feet. The analysis encompassed elemental composition, chemostratigraphy, and mineralogy. Chemostratigraphic zones were identified based on distinct changes in chemical and mineralogical profiles, marked by specific elements and key ratios. These zones are expected to be consistent over significant distances, at least within the length of the horizontal wellbore, and should be easily identifiable in the cuttings. Near real-time formation evaluation was achieved with a controlled rate of penetration (ROP) of 10 ft/hr, allowing XRF data to be obtained just 5 feet behind the bit while sliding and 10 feet behind the bit while in rotary mode. With the LWD signal trailing at 45 feet, elemental data from the XRF was instrumental in pinpointing the top of the targeted sub-layer and successfully landing the well. The ability to clearly and precisely identify formation tops in the sub-layers provided a solid basis for geo-steering the lateral section.
Advanced cuttings analysis played a crucial role in geo-steering the well, especially in areas where the LWD gamma ray (GR) signature was ambiguous and in a 485-foot section with no LWD signal. This approach also helped avoid lost time and costs from unwanted trips due to third-party tool failures, estimated at 36 hours. The well was tested with excellent oil flow, demonstrating that advanced cutting analysis (XRF and XRD) effectively supported real-time geo-steering in slim-hole scenarios where LWD capabilities are limited and uncertain.
