Identification and interpretation of fractures, bed boundaries, and borehole breakout from high-resolution images plays a crucial role in optimizing completion design. In low-angle wells drilled with oil-based mud (OBM), images may be acquired using wireline. However, using wireline has been a challenge when inclinations exceed 45°, making logging-while-drilling (LWD) acquisition preferable. This paper presents the first use of a 4¾-in. ultrasonic LWD service to provide high-resolution images to assess fractures in the Marrat formation in North Kuwait. This paper presents LWD log data and high-resolution acoustic amplitude images used to evaluate carbonates within the Middle and Lower Marrat formations and describes their input into the design of the completion program. The 4¾-in. ultrasonic imaging tool was placed within a complex bottomhole assembly (BHA) composed of density and neutron porosity, acoustic, and nuclear magnetic resonance (NMR) sensors. The methodology used to create high-resolution images for both drilling and wipe run data sets using the logging speed and tool rotation is detailed, along with a description of how the image interpretation was used to optimize the completion design. The 6-in. borehole sections of the Middle and Lower Marrat formations are known to have prominent open fractures. During drilling, significant mud losses were encountered which required a reduction of mud weight to stabilize the well. From the memory data, 256-sector acoustic amplitude images were interpreted to provide an initial assessment of fractures and geological features. It was observed that an interval of log where mud losses were believed to have occurred corresponded with a large fracture and borehole breakout. In addition, multiple sections of borehole breakout at the top and bottom of the borehole were observed, with bed dip interpretation supporting the known field structure. Further post-well processing of the acoustic amplitude data was performed which created enhanced-resolution images. The processing method takes all of the raw impedance measurements–up to 2000 acquisitions per second–and re-sectors the data based upon the logging speed and tool rotation. The resulting images (540 sector for the drilled section and 360 sector for the wiped section) enabled identification of 255 features over the logged interval. The interpretation of fractures, their location, and dip and strike directions were used to optimize the completion design. The ability to acquire high-resolution LWD images in OBM applications within high-angle 6-in. hole sections to identify a wide range of features, including fractures, bed boundaries, and borehole breakout, represents a first in Kuwait. Removing the need to use wireline logging technologies in high-angle wells with wellbore stability concerns helps to reduce well time and logging risk. Deliverables from the 4¾-in. ultrasonic imaging service provide direct input into completion design, helping to optimize production.

An operator in the Middle East had several corrosive high-pressure wells which were shut in due to stuck coiled tubing. The well design and status eliminated options for conventional work-overs, so the fish had to be recovered to surface utilizing a Hydraulic Workover Unit and specialist Thru-Tubing fishing equipment. This required highly experienced fishing & milling personnel who could ensure the correct equipment was used for each run-in hole, thereby enabling a safe and efficient operation. Successful execution was based on detailed up-front planning and application of thru-tubing well intervention services for high pressure/high temperature (HP/HT) conditions. The ideal operation would include selection of the right personnel, technology and bottom-hole assembly (BHA) configuration that would offer: Built-in contingencies for pressure control. Meet the material selection guidelines for operations in the corrosive environment. Allow for adequate consideration for all possible contingencies that may arise during the operation. Following this careful up-front planning, more than 1,082 runs were carried out in 15 wells. More than 68,000-ft of coiled tubing, with sizes ranging from 1.250in. -1.750in, was recovered to surface. In total, more than 42,664 man-hours were completed with Zero LTIs and Zero NPT. This paper serves to highlight the value that competent up-front planning, equipment selection and choice of personnel adds to an extremely high profile and complex fishing campaign. This allowed complex fish to be recovered, restoring production without the need for a costly work-over operation and ultimately saved the operator from major expense.

Traditionally, 12.25-in. hole sections in the Jurassic formations were planned to be drilled with mud weight (MW) of 20 ppg and solids content of 45%. The planned drilling would use a rotary assembly from the Hith formation, crossing several zones in which mud losses or gains were likely. The casing would then be set in the thin shale base of the Gotnia formation. A minor inaccuracy in casing setting depth could often lead to well-control issues. Pore pressure drops severely below the shale base and requires a MW of 15 ppg. Passing this shale base can lead to severe losses and potential abandonment of the well. An anhydrite marker is located approximately 50 ft above the shale base. To reduce risk, the operator would normally drill to this marker at a rate of penetration (ROP) of 20-30 ft/hr, then decrease the ROP to 2 ft/hr. While slowly drilling the last part of the section, penetration would be stopped every few feet to circulate bottoms-up to receive samples confirming the shale base; this process requires an additional 24 hours of rig time. After reaching the casing point, the operator would pull out of the hole to pick up logging-while-drilling (LWD) tools to perform a wiping run. This logging, however, is frequently cancelled because of wellbore stability issues, resulting in the loss of important formation-evaluation data across this interval. A new solution has been developed, comprising drilling with a rotary assembly to the final anhydrite marker, then pulling the string out of hole to pick up LWD triple-combo and sonic tools, with a conventional gamma ray sensor placed only 6 ft from the bit. The remaining part of the section would then be drilled at 7-10 ft/hr until the gamma-ray tool detected the shale base, thereby determining the casing depth. In addition, it was planned to re-log the previously drilled interval. This solution prevented the well from potential abandonment and reduced drilling time. It also secured critical formation evaluation data for exploration and future field development. The engineered drilling solution was tried for the first time in these formation sequences within a harsh drilling and logging environment. The option of rotary steerable services with an at-bit GR sensor was not considered because of the high cost.

Directional wells through the 6-in. production-hole sections in the Marrat Reservoir of the Jurassic formations have traditionally required several wireline-logging and hole-conditioning runs for comprehensive petrophysical interpretation and completion design. As the planned well inclinations increase to maximize reservoir exposure and sweep efficiency, wireline deployment poses significant challenges due to the increased risk of losing the bottomhole assembly (BHA) in the hole. Over time, logging-while-drilling (LWD) tools have become preferable for the asset team, where the tools are run either in the drilling BHA or during a dedicated wiper trip after the section has been drilled to total depth (TD). Using LWD tools in this application also reduces well delivery times and costs. A comprehensive logging solution was required to drill the 6-in. reservoir section of a study well. The complex LWD string, consisting of gamma ray, resistivity, neutron porosity, azimuthal density, azimuthal sonic, and nuclear magnetic resonance (NMR) tools, was deployed on a motorized rotary steerable system (MRSS) BHA. In addition, a prototype high-resolution acoustic imaging and caliper tool, designed to be run in both water-based mud (WBM) and oil-based mud (OBM), was also included. The acquired logging data were used for enhanced formation evaluation. Fracture and borehole breakout interpretation from the image data played a key role in the successful completion design. This ultimately led to Kuwait’s first successful “hexa-combo” LWD drilling run and the country’s first LWD ultrasonic imaging tool run in OBM in this hole size, with 13.3 ppg OBM with a maximum downhole temperature of 275°F.