Optimization of drilling performance with low-risk technologies has become the main challenge for Abu Dhabi Onshore Operator. This paper presents a step change in the drilling operations with the successful deployment of a proven technology solution (of wellbore clean up scrapers which can be added to the drilling assembly) in the new wells, allowing an improvement of the well's drilling time by 1-1.5 rig days for each well. Following the successful implementation in Abu Dhabi Onshore pilot wells, deployment of the Scraping While Technology (or, SwD) in the new wells have now become part of the standard operations, bringing in direct savings of 65 million-USD to the Operator. The proposed innovative application allows to combine the wellbore clean up scrapers for 7 inches liner and 9.625 inches casing as part of the drilling Bottom Hole Assembly (BHA) for the last open hole section (6 inches or 6.125 inches) of the well. The Scraper While Drilling tools are dormant while the drilling activity is ongoing and can be hydro-mechanically activated on-demand by dropping steel balls from surface at the end of the drilling activity. Upon activation, the scraper blades from the SwD tools extend outwards and push against the ID (inner diameter) of the casing or liner. The solution allows scraping the casings and liners across the completion packer setting depths while pulling out of the drilling assembly and thereby leaving the completion interval ready for either recording the cased hole logs or running the completion jewellery. This implementation of the SwD saves the operator between 1 to 1.5 rig days per well by allowing the operator to cancel dedicated clean out scraper run(s). There is no limitation for Scraper While Drilling deployment with regards to the horizontal hole section lengths. Using the SwD in the drilling assembly eliminates the need for a dedicated well bore clean out conventional scraper run; it also reduces the risk factors by eliminating the pickup, lay down, run in hole, and pull out of hole activities of the dedicated well bore clean out runs with conventional scrapers. The Scraper While Drilling technology hence revolutionizes a typical well design and its drilling operations by eliminating dedicated clean out scraper runs with conventional scrapers and allowing the operator to drill more wells based on the days saved per well in a long-term drilling campaign.
Underbalanced Drilling (UBD) has become a popular technique in oil & gas industry, especially for well-developed hydrocarbon fields to minimize formation damage and maximize productivity. The key in UBD is to control bottom hole circulating pressure (BHCP). To maintain BHCP lower than the formation pressure, a light weight drilling fluid has to be used and probably with concurrent N2 injection. In the case of a tight reservoir, N2 injection rate is increased as high as 1500 SCFM, which will cause severe gas slugging and dramatic standpipe pressure (SPP) reduction when the gas is circulated though the choke. MWD signal will then be lost due to the pressure fluctuation. This paper will present a BHA optimization solution to maintain sufficient and stable SPP during UBD. Two UBD cases will be discussed. Two main challenges were encountered in the first well: one was to reduce BHCP sufficiently low, the other was to maintain SPP high and stable. To reduce the BHCP, MWD pulser was changed from 180-280 GPM rating to 150-250 GPM to allow lower drilling fluid flow rate and increased N2 injection rate to 1500 SCFM. However, surface SPP dropped significantly due to gas slugging. To avoid this happen, the following optimizations were implemented in the second well: 1) added more HWDPs to reduce internal diameter of the drill string; 2) reduced bit TFA by using less nozzles; 3) installed flow rate restrictor in the drill string. With reduced flow rate and increased N2 injection rate, BHCP was reduced to 300 psi below formation pressure. At the same time, with the optimized BHA, surface SPP was increased sufficiently to transfer MWD signal continuously. According to the simulation, among the 600 psi increase in surface pressure, 300 psi was from the restrictor, 150 psi was from the change of bit nozzles and 150 psi was from the added HWDPs. The main contribution was from the restrictor. Compared with the first well, which was drilled without restrictor, the data retrieved from the second well was smoother and more readable. It was the first time that downhole flow restrictor was used in UBD well to maintain SPP. Combined with adding HWDPs and reducing bit TFA, SPP was increased sufficiently, whereby enabled continuous signal transmission and better data quality. Therefore, it is recommended to use this technique in the next UBD campaign.
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