Efficiently drilling the 16" hole section in high temperature/high pressure (HTHP) conditions through hard/abrasive Jurassic formations in Kuwait's oil fields has been a distinctive challenge for more than a decade. The difficult sequence of lithologies starts with abrasive Zubair sand (with pyrite) followed by reactive Ratawi shale and then hard carbonates (UCS 10–30kpsi). The Zubair is approximately 1300ft thick and has historically been drilled with four/six rollercone TCIs or a combination of two TCIs and two PDC bits or two/three PDCs. The objective has been to reduce the total number of bits/trips and ultimately drill the Zubair and as much Ratawi as possible with one PDC bit. Initial attempts with PDC were encouraging, but not economically successful compared to rollercone cost/ft. To improve performance, an FEA-based modeling system was used to predict downhole behavior. Based on these knowledge gains, a new PDC bit design was produced with optimized blade orientation and reconfigured cutting structure. Although the new design did improve performance, the drilling team concluded the PDC shearing elements were unable to withstand the HTHP environment (thermal degradation) and vibration induced impact damage. The operator required new technology to enhance cutter longevity. To deliver a suitable solution, new cutter technology was developed using a two-step manufacturing process high temperature/high pressure pressing technique. Laboratory tests indicated the new style cutter has significantly increased resistance to abrasive wear and thermal fatigue compared to standard cutters without compromising impact resistance. The HTHP cutters were run in a nine-bladed PDC with outstanding results setting a new Kuwaiti single run Zubair footage record (1302ft) and Zubair/Ratawi field footage record (1347ft). The authors will discuss the application challenges and resulting performance improvement. Offset analysis will document a performance step-change that saved the operator an average of 10 days of rig-time (﹩500,000USD).
The 16′ Vertical Performance Motor Section is the most challenging section in Exploration Deep Drilling in Burgan Field & All South East Kuwait. The section comprises drilling hard and abrasive Zubair formation followed by reactive Ratawi Shale formation. Several technologies were introduced during the last ten years in search of an economic solution to deliver this section safer and faster with limited success. The objective of this paper is to present the process and technology implemented to drill Zubair and Ratawi Shale formations in two different wells with the same bit at record rates of penetration. Bit durability is generally the main driver in the 16′ section performance. Historically, one to two polycrystalline diamond compact (PDC) bits were utilized in this section and were pulled out for low penetration rates. The new solution required a thorough offset data analysis, including formation porosity, rock strength and abrasiveness analysis, applied drilling parameters and Mechanical Specific Energy (MSE) analysis using software. A customized PDC bit design was then developed using a state of the art bit/formation interaction model combined with an advanced cutter technology and hydraulics pairing for ultimate cutter cooling. The new PDC bit design and the implementation of the softwares used to analyse offset wells drilling parameters and rock mechanics had a significant effect on the bit durability and Rate of Penetration (ROP). The optimized drilling parameters applied as per the former set roadmap aided in managing the bit cutting structure through Zubair and Ratawi Shale formations and the bit was pulled out in re-runnable condition with a new field ROP record. The same bit was then used again in different well and drilled Zubair and Ratawi Shale formations and pulled out with 1, 3 dull condition. Over the two wells drilled, the optimized drilling plan saved National Oil Company over US $200,000, reducing the cost per foot (CPF) drilled by 38% over the field average CPF, increasing the ROP by 55% over the field average and drilling 69% footage more than the previous section benchmark footage. With the engineering evaluation of the offset data and the utilization of the new bit design, National Oil Company managed to drill Zubair and Ratawi Shale section in two different wells with the same bit for the first time and was able to improve drilling efficiency and cutting the drilling cost by eliminating bit trips and cost of new PDC bits.
In Kuwait's largest reservoir, the Burgan Field, exploration wells have large potential for drilling optimization and savings; specifically a 22 inch hole, that is drilled conventionally using multiple roller cone bits in multiple trips through challenging inter-bedded formations. Hybrid drill bit technology, roller cone combined with Polycrystalline Diamond Compact, was introduced in search for an economically viable solution to deliver wells faster and achieve yearly operator targets. This paper analyzes the breakthrough drilling performance achieved by a 22 inch hybrid bit in comparison to conventional roller cones offsets and provides conclusions on economic viability. The main challenges drilling the 22 inch section are drill bit durability and drilling vibrations through inter-bedded formation layers of limestone, shale and sandstone. In addition to curing fluid losses in certain porous formations that negatively affect Rate Of Penetration (ROP). Typically two roller cone bits are used on rotary drive to drill this section at 15 feet per hour, consuming seven drilling days. Using Polycrystalline Diamond Compact (PDC) bit with a performance motor to increase ROP performance is not an economically viable solution. Using hybrid drill bit on rotary drive combines the benefits of PDC blades' durability and higher cutting efficiency with the cones' stability by grinding and gouging into the formation. The deployment of the hybrid technology was a collaboration project between a national oil company and a major oil services company. The teams focused on optimizing the complete drilling system including the bottom hole assembly, hydraulics, drilling parameters and geological factors to match the hybrid drill bit mechanism. The hybrid design selection and drilling optimization resulted in a 142-percent ROP improvement from offsets average performance. The hybrid designs consistently drilled the 22 inch hole after casing shoe to section total depth at 31 feet per hour, using one bit, in three drilling days in comparison to seven days average performance. The total operator savings from e section was approximately USD 175,000 in the first deployment. The second and third deployments established performance consistency. Such remarkable economical savings and technical optimization proved that the hybrid technology is the viable solution for two prolific exploration applications.
Since the spudding of the first well in the Burgan Field in 1937, continuous improvements have been made in the drilling of wells in Kuwait. This paper will address the drilling optimization performance that has occurred during the development of the deeper high pressured formations. Continued optimization performance in the deeper high pressured wells has proved to be the greatest challenge as a result of the adverse geological environment that has had to be addressed while drilling. This adverse geological environment consists of salt/anhydrite sections where formation pressure nearly equals fracture strength, pressure reversals, highly fractured thief zones and the presence of H2S. While there was some earlier deep drilling in Kuwait, development of the deeper high pressured horizons began in earnest in the early to mid 80's and is still ongoing. Four major field studies will be addressed in the paper which encompasses the majority of the deeper high pressure drilling activity. The inherent problems that had to be overcome, the solutions that were found and the problems still to be faced will be depicted in this paper. Abduliyah Field drilling has improved by a reduction of 77% in drilling days over a 12 year period. Magwa Field drilling has improved by a reduction of 58% in drilling days over a 10 year period. Minagish Field drilling has improved by a reduction of 74% in drilling days over a 14 year period. Umm Gudair Field drilling has improved drilling by a reduction of 72% in drilling days over a 13 year period. Total well depths for the above fields has ranged from 11800' to 16800'. Improvements which will be detailed in this paper will include well design changes, methods dealing with lost returns, mud cap drilling, bit optimization, and others. Introduction Oil development in Kuwait had been limited to the Cretaceous and Tertiary formations prior to the late 70's. Exploration wells drilled into the Jurassic sequence in the late 70's and early 80's discovered oil in several of the Jurassic formations. As a result of these discoveries, development drilling for the Jurassic formations began in earnest in the early to mid 80's. Within Kuwait the Jurassic sequence is the beginning of increased formation pressure. An extensive drilling program into high pressured formations proved a tremendous challenge. As a result a tremendous amount of learning took place during the initial drilling phases. The lessons learned from earlier drilling was utilized in development of improved drilling programs and job execution. This paper will address the problems encountered, lessons learned and solutions developed while developing the Jurassic productive formations. Background of Tertiary, Cretaceous, & Jurassic Sequence Before discussing the drilling of the Jurassic section some background is needed regarding the normal pressured formations uphole. The Cretaceous and Tertiary sequence which up to the late 70's was Kuwait's primary interest consists primarily of sands, shales, and limestones all normally pressured. The shale intervals are highly reactive and require inhibitive drilling fluids to prevent hydration and sloughing. The limestones for the most part vary in degrees of fracturing with the more fractured zones proving to be extremely high thief zones. The worst thief zones occur near the surface (Dammam) and in the Cretaceous sequence (Shualba). These drilling issues had to be addressed in the drilling program prior to entering the higher pressured Jurassic sequence. The Jurassic sequence is made up of formations that include fractured & oolitic limestones, salts, anhydrites, grainstones and shales. Formation pressures run from 11.0 ppg up to just below 19.0 ppg. The Jurassic section of interest ranges in thickness from 2300' to 3100'. P. 205^
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