Objective/Scope The objective of this paper is to present a successful acid frac technique applied in a deep HPHT well to enhance the productivity of Marrat reservoir. Method, Procedures, Process Jurassic reservoirs in the state of Kuwait are deep, sour and tight with High-Pressure and High-Temperature (HPHT) environment. Challenging reservoir quality like low permeability, low porosity, uncertainty about some natural and induced fractures, high stress, etc limits the productivity development for this reservoir. The subject well was drilled up to 16,790 ft with high-density Oil Base Mud (OBM), upto 17 ppg, targeting Marrat formation to prove hydrocarbon in this area. Formation damage caused due to invasion of high-density mud, using Barite as a weighting agent, into the carbonate reservoir poses a challenge to design a proper stimulation treatment to restore the permeability and to evaluate the real reservoir potential. Since the damage caused by OBM invasion cannot be easily treated, it was decided to stimulate this reservoir either by matrix or fracture stimulation. The subject well was tested with Drill Stem Test (DST) and perforated in underbalance condition using TCP gun. Acid treatment was performed with 28% emulsified acid solutions to gain the deep wormhole penetration in order to enhance the well productivity. Pre and Post stimulation flow measurement confirmed a slight improvement in productivity. But still there is a scope for increasing productivity further more. Based on the test results, it was decided to Hydraulic Frac the Jurassic reservoir to achieve the expected potential. A detailed study was carried out to identify reservoir quality and completion challenges that limit the development of reservoir potential and to recommend remedial mechanism, acid or proppant frac, to improve the well productivity. Based on the analysis, acid frac design and procedure was established to gather data and improve productivity from Marrat reservoir. Prior to the main fracturing treatment, a data-frac was conducted to determine reservoir parameters such as fracture extension pressure, fracture closure pressure and instantaneous shut-in pressure. Based on data-frac results, acid frac was successfully executed and the well productivity was tremendously improved. Results, Observations, Conclusions High injection surface pressure of 13,800 psi and high leak-off was observed during main acid treatment due to the tight nature of the formation that resulted in low fluid efficiency and relatively short etched fracture length. Acid fracturing treatment was carried out successfully without encountering any major operational issues. The post-acid frac production results show significant improvement in productivity Index(PI) and 3-4 folds increase in production comparing to main acid treatment results. Post-frac analysis was carried out on the sustained production from the Jurassic reservoir. Novel/Additive Information Improvement in well productivity after the acid frac stimulation confirmed the well potential and supported exploration group to achieve the reserve target.

Simulating the mechanical response of PDC drill bits contains a lot of uncertainties. Rock and fluid properties are generally poorly known, complex interactions occur downhole and physical models can hardly capture the full complexity of downhole phenomena. This paper presents a statistical approach that improves the reliability of the PDC bit design optimization process by ensuring that the expected directional behavior of the drill bit is robust over a well-defined range of drilling parameters. It is first examined how uncertainty propagates through an accurate bit/rock interaction model which simulates numerically the interaction between a given PDC drill bit geometry and a given rock formation, both represented as 3D meshed surfaces. Series of simulations have been launched with simulation parameters defined as probability density functions. The focus has been set on directional drilling simulations where the drill bit is subjected to significant variations in contact loads on gage pads along its trajectory. A global sensitivity analysis has also been performed to identify the key parameters which control drilling performance. Directional system parameters are critical in terms of steerability and tool face control, particularly in high dogleg severity applications. Based on these simulations, a statistical optimization strategy has then been implemented to ensure that the directional performance of the drill bit remains effective under a given uncertain drilling environment. Statistical analysis combined with drilling simulations indicated that ROP improvements could even be achieved without compromising steerability. A balanced bit design was selected and manufactured in an 8 1/2-in. model to drill a 714 ft section of a Kuwait field. The bit was run on a high dogleg rotary steerable system and directional assembly. The bit achieved the high steerability goals required by the application while showing a good compatibility with the directional tool. Moreover, ROP was increased by approximately 27% compared to offset wells, setting a record rate of penetration in the field. Whereas statistical analyses are commonly conducted in the field of geosciences, it has rarely been applied in the field of drilling applications. The statistical bit design optimization strategy deployed in this work has allowed to improve both the drilling performance of the drill bit and its reliability.

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.

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Cement quality is an important well integrity consideration to ensure proper hydraulic sealing. Traditionally, wireline cement bond logs have been used extensively in the Jurassic formation of North Kuwait. The case study well presented in this paper had an 80° inclination and 3,000 ft of a 6-in. open hole, which has remained opened for quite some time. Cement evaluation was required inside the 7 5/8-in liner to determine the cement quality behind the liner and integrity of liner shoe. This information is important for achieving a successful of multistage completion for the producing interval in the 6-in open hole. The target interval had a vertical depth greater than 14,000ft from mean-sea level with a well deviation more than 80°. Four operational days were required to run drill pipe conveyance of conventional cement evaluation wireline tools. This operation would have exposed the 2,500ft of open hole to potentially collapsing situation due to the time dependence of the wellbore stability. The capability of logging-while-drilling (LWD) multipole sonic tool for evaluating the cement quality was considered, as there was plan to acquire open hole log data using LWD technology, which included the LWD multipole sonic tool. While running in the hole to the open hole section, the LWD multipole sonic tool can acquire sonic-based cement evaluation data inside of the 7 5/8-in liner. This operating method consumes no rig time while obtaining the well integrity information. This paper presents the case study, along with the LWD multipole sonic tool theory for measuring cement bond quality index, operation preparation, and the results of the data acquisition.