In April 2012, the world's first 16-in. solid expandable tubular (SET) liner was run to depth and successfully cemented and expanded. The installation of the large diameter liner marks a significant shift in the application of expandables from deeper contingency applications to planned hole-conservation designs in the upper wellbore. The purpose of the installation was zonal isolation. In Saudi Arabia, the Uthmaniyah field, the prolific Arab D reservoir has been produced for many years, resulting in lower pore pressures than the shallower Arab A, B, and C reservoirs. Due to the differences in pore pressure, isolation between the Arab D and Arab A, B, C reservoirs is required to efficiently drill some of these wells. The 16 × 18-5/8-in., 115 lb/ft open hole liner (OHL) system isolated the Arab D reservoir by covering the Arab A, B, and C reservoirs while minimizing the loss of hole diameter to maintain the original wellbore design and drilling tools. Both objectives were safely and successfully achieved with the running and expansion of 1,708 ft (pre-expanded length) of 16-in. solid expandable pipe, hung as a liner and anchored into the 18-5/8-in. casing. To isolate the pressure differential, the 16-in. SET liner was installed in a negative pressure environment. Once the liner was installed, the mud weight was reduced to drill the lower pressure Arab D reservoir and the remainder of the hole section. From a reservoir management viewpoint, this installation eliminated cross flow from the higher pressure Arab A, B, and C into the Arab D reservoir, thus preserving the pressure regime of the oil producing Arab D. Additional benefits of the 16-in. expandable liner included an increase in ROP in the hard rock environment, the elimination of two-stage cementing requirements and the associated risk of stage tool failure, and reduction of hook load requirements associated with large, long casing strings.
Saudi Aramco's first medium radius horizontal sidetrack gas well, Haradh-AX1, was drilled and completed in June, 2008 in a record time of 48.7 days with 4,989 ft of reservoir contact and a 33% reduction in overall cost. The previous, Khuff-C Horizontal sidetracks which included the same operations; de-completion, sidetracking and re-completion, averaged 83 days with 3,441 ft of sidetracked lateral across the Khuff-C. Directional drilling in the medium radius lateral after building at 12°/100 ft to a sail inclination of 88° was characterized by better bit performance, lower torque and drag, improved wellbore stability and steerability. In the previously employed long radius horizontal sidetrack design, extensive milling operations were required to gain access to the 8-3/8?? open hole to sidetrack. The 8-3/8" long radius build section would then be drilled from the Base Jilh Dolomite, across the troublesome and sometimes abnormally pressured Lower Jilh and Sudair Shale formations to the top of the Khuff-C where a new 7?? liner would be run and cemented. The 5- 7/8?? lateral would then be drilled across the Khuff-C and an open-hole completion run. In the medium radius design, the sidetrack (ST) could be made deeper, in the same pressure regime, by cutting a ST window in the existing 7?? liner 450 ft true vertical depth (tvd) above the Khuff-C target reservoir, kicking off and drilling 5-7/8?? hole across the Khuff-C to total depth (TD). This paper further details the time and cost savings possible from the application of proven medium radius drilling technology from Saudi Aramco's Arab-D Horizontal Oil wells produced from 6,500 ft tvd to the deep gas wells produced from the Khuff formation at 12,000 ft tvd, a new drilling environment. More medium radius horizontal sidetracks are planned and a similar medium radius Khuff-B Horizontal ST, ANDRAX1, which built at 32°/100 ft, was just successfully completed at 14,819 ft with a 2,400 ft horizontal section. Introduction Previously, a total of nine horizontal re-entry/sidetracks were performed on existing poor to non-producing gas wells in the Ghawar field of Saudi Arabia owned and operated by Saudi Aramco. The general procedure was to mill out the 7?? liner overlap (500 ft -1100 ft) to around 150 ft below the 9-5/8?? shoe. The milling was extremely tedious and time consuming because of milling related problems such as the formation of " bird's nests?? (packing off of swarf in the milling annulus), stuck pipe, inconsistent mill performance and difficulty maintaining milling fluid low-end rheology. A cement sidetrack plug would then be set in the 8-3/8?? open hole, after which the sidetrack would be kicked-off with a long radius build trajectory (typically 3 to 7°/100 ft) to the top of the Khuff-C formation and a new 7?? liner was run and cemented in place. Once the usually higher pressured by as much as 2,400 psi, Khuff-A & Khuff-B formations are cased off, the 5- 7/8 in. section of the long radius trajectory would continue building inclination to about 90° across the target producing zone; the Khuff-C; using the minimum required mud weight to drill to TD.
Saudi Aramco recently drilled a gas well using Managed Pressure Drilling (MPD) as part of its exploration program. This well was the third exploratory well drilled with the objective to test the hydrocarbon potential of the sandstone reservoirs of Lower Permian era. Since a narrow drilling window between the reservoir gradient and the fracture gradient was expected, Constant Bottom-hole Pressure (CBHP) variant of MPD was planned to be utilized in this well. There was no Nonproductive Time (NPT) during the MPD phase, hydrocarbon gas from the target formation was measured by the Gas Chromatograph (GC) and properly circulated out via the Automated MPD Control System without the need of conventional well control procedures. Average Rate of Penetration (ROP) increased by three-folds compared to the nearest offset well. Based on the real-time GC analysis, four zones within the target hole section show the most potential for hydrocarbons and further delineations are being planned for these intervals. This paper summarizes Saudi Aramco's experience gained during the drilling of this well. It further highlights the operational complexity and the challenges faced during the implementation of this technology while drilling the exploratory well with very little offset information. The paper also elaborates on the lessons learned and how they were implemented continuously with regards to Health, Safety and Environment (HSE) during the MPD operations. It is concluded that the use of an Automated MPD control system integrated with GC in Saudi Aramco's deep gas drilling project represents a technological improvement that will enable the company in achieving its goals in a safer and a more efficient manner.
An inventive application for Roller Cone (TCI) and Polycrystalline Diamond Compact (PDC) bits (all sizes) that involves reusing the bits in future wells for similar well design types. With factory drilling being carried out in one of the Gas field (among other areas in gas) with over 50 runs a year provides an excellent opportunity to utilize rerun bits, both TCI and PDC, that have a 90-95% life remaining. Using this approach provides an effective and efficient way of cost saving during drilling. While the cost of new bits in the country is very high compared to markets outside, mainly due to logistics issues with recent and continuous enhancements in bit designs, it makes complete sense to reuse these bits; especially when a huge inventory is available due to so many rigs drilling the similar type well designs in one or similar gas fields. The main criterion is to keep a track of all sizes of bits used on all gas rigs in the area and in the tool house (warehouse). Often, a particular size bit, either TCI or PDC, is used to drill a very short interval in a particular section due to a technical reason for the bit in the well being pulled out of hole, and is almost in brand new condition. Having an up-to-date inventory of these bits from the gas rigs, the tool house, and bit vendors makes it easy to identify such bits and utilize them in new wells, which provides significant cost savings. Using the rerun bit approach immediately takes the bit cost for that particular hole section to 0$ and so we can achieve additional drilling optimization by utilizing a mud motor in that section, i.e., 12-in., 8-3/8 in., or 5-7/8 in., and further increasing the rate of penetration (ROP) by maintaining the same cost/ft ($/ft) in the section and even breaking bit record runs. In the last few wells it has been evident that by using this approach, the cost/ft for the 12-in. section drilling in the Gas Field field is seen as low as 52% of the new bit for the same year; providing a benchmark for the field. This would not have been possible without utilizing the rerun bits from previous wells. This approach is proving to be very beneficial. As a result of a number of these TCI and PDC bits available in reusable condition as a result of a large number of wells drilled every year in gas fields, significant cost savings have been achieved, which translates into millions of dollars in savings. The rerun bits have substantial advantages over the new bits, primarily due to cost savings and enhanced bit designs with high durability and bit life over the last decade. For particular application in gas drilling, it is clear that having a large inventory of rerun bits available for almost all hole sizes will enable drilling cost optimization.
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