Deep gas drilling in carbonate environment is very challenging due to elevated temperatures with pressures. Additionally, the presence of the shock and vibrations across the interbedded layers of limestone and dolomites. Over the years different drilling techniques are employed for improving the drilling performance. The analysis of the data showed that the wells where the shock and vibrations were lower the optimum performance was achieved and the section was drilled in one run compared to the wells where multiple runs were required because of shock and vibration. Further analysis showed that the Shocks are not only seen while drilling, but the level of shocks was high during non-drilling activity such as reaming during wiper trips, back reaming across tight spots and before reaming while connection. This paper will cover the techniques that were employed to minimize the S&V or at least reduce to the minimum acceptable level where the drilling performance can be achieved. Understanding the shock and vibration across different formations and sub layers within formation. Comparison of shock and vibration for different BHA's while drilling. Application of the stat of the art drilling dynamic simulator. Comparison of BHA's with standalone and motor power Rotary steerable system. Identifying and developing the strategy while crossing the interbedded layers. Feedback to the reliability team for improvement. Based on understanding the shock and Vibration, and lesson learned multiple wells are drilled where the number of BHA's used to drill the section are reduced and the ratio of drilling the section in one runs is increasing.
The intelligent drilling system (IDS), based on the 57,000 bits per second and bi-directional wired drill pipe telemetry, has been under experimental trial in the industry in a variety of applications. Several SPE papers have covered these applications, which include: drilling optimization, hole cleaning, drilling risks and NPT reduction. The IDS can also be utilized with other tools to expand the window of drilling optimization applications to include the risk management approach, where the system value and the impact on drilling operations will be greater. To achieve this change, it is important to expand and improve the current techniques and develop new methods that will expand the application of the wired drill pipe (WDP) system. This paper will describe the application of WDP in middle east during a trial test, showing how it was expanded and customized to suit complex drilling environments. This field trial involved a three-phase approach. Each of these phases tested the functionality and application of the IDS to determine the potential benefit for different projects. Phase 1 aimed at testing the system functionality and integrity. This includes along string measurements (ASMs), logging while drilling (LWD) data transmission, wired bottomhole assembly components, top drive and surface system, and interface sub and signal boosters. Phase 2 aimed at testing the top-of-mud measurements derived from the ASMs pressure readings. The objective was to test the algorithm and validate the results to ensure accurate readings. Measuring the fluid level is critical in managing total loss situations. Phase 3 aimed at early kick detection simulation. In this phase, a kick was simulated by pumping a heavy mud pill and checking ASM response while the pill was progressing up the annulus. This simulation has important applications in early downhole kick detection in total loss situations where there are no returns to surface. Finally, the paper will outline future applications of the IDS in managing risk in complex and risky drilling environments. This is where total losses are encountered while drilling across high-pressure reservoirs. Fluid level, in total losses situation, will be monitored by high-frequency downhole pressure measurments at multiple depths. These measurements of the downhole hydrostatic and dynamic pressure will also be providing early kick detection.
Generally, deep gas workover/re-entry wells in Saudi Arabia are kicked off in the Sudair formation through a whipstock because the overlying base Jilh dolomite can flow with high pressure, which jeopardizes well control. Whipstocks are set deep in the 9 5/8-in. casing, after which the 8 3/8-in. and 5 7/8-in. holes are drilled to access the target Lower Carbonate and Sand reservoirs. Deeper kickoffs also avoid contact across the water-bearing Carbonate A, aiming for displacement across Carbonate B or C reservoirs. Isolation from Carbonate A is important for multistage fracturing completions as they are still not proven for the long-term isolation of water-bearing zones. Regardless of the deeper whipstock setting, the high dogleg requirements exceed the capabilities of conventional rotary steerable systems (RSS). Conventional steerable motors with high-bend housing and 70 to 80% of the sliding mode of drilling has been the only option to achieve such high dogleg severity (DLS/100ft). Drilling medium-radius wells with a conventional motor assembly requires multiple runs, wiper trips to clean the hole, and multiple reaming trips before running the liner. These operations result in poor drilling efficiency due to slow penetration rates and bit trips. A high build rate rotary steerable system (HRSS) was introduced as a solution for such challenges in the 8 3/8-in. and 5 7/8-in. sections. While the HRSS technology has been used before, this was the first time the HRSS kicked off vertically from a whipstock in Saudi Arabia or worldwide. The new technology allowed the kickoff point to be pushed further into the Sudair formation near the Sudair dolomite, reducing the risk from Jilh pressure and associated cost. The step change provided the option to slim the hole by eliminating the 8 3/8in. hole size, and kickoff was done in the 7-in. liner. Deployment of the HRSS allowed directly kicking off from a whipstock set vertically, eliminating the need for a dedicated steerable motor assembly run. Direct kickoff also meant eliminating the need for gyro tool for steerability, because conventional RSS tools could only be used outside the zone of magnetic interference, once sufficient separation from the mother bore was achieved. Consistent doglegs of more than 14°/100 ft were recorded; and the maximum dogleg was 17.44°/100 ft. Since then, this concept has been applied to other vertical re-entry wells and at an existing inclinations successfully in the 8 3/8-in. and 5 7/8-in. sections in Saudi Arabia and worldwide. The scope of the paper is limited to wells in Saudi Arabian deep gas wells only. The average rate of penetration (ROP) across this build section shows a 137% improvement over the ROP for conventional motor bottom-hole assemblies (BHA) for similar build sections. Eliminating the 8 3/8-in. section, avoiding the hazards of drilling in Jilh and Sudair formations, saving the motor trip to kick off from the whipstock, and improving ROP resulted in significant savings. This step change in drilling performance was realized by a thorough understanding of local drilling conditions and indepth analysis that enabled efficient execution.
During the field-development life of a mature extended-reach drill (ERD) project, a wide range of drilling tools and practices were introduced to continuously improve drilling performance and well delivery times. One of the main challenges encountered in the ERD wells was in the 12¼-in. curve section, and drilling through interbedded hard layers with severe downhole stick/slip and downhole vibrations. Historically, both motor and motorized rotary steerable system (MRSS) bottomhole assemblies (BHAs) were used to drill this section. However, the motor BHA's lower rate of penetration (ROP) and weight transfer problem cause it to be an economically inefficient strategy in contrast with the MRSS BHA, successfully drilled through all of the challenges with higher ROP and a relatively lower overall cost. Driven by cost reduction necessity, an intensive engineering effort was implemented by the operator and service provider drilling engineering teams to change the motor BHA into a cost-effective drilling strategy for the challenging 12¼-in section. Analyzing the design and performance of all previous motor BHAs led to identifying the main challenges. Detailed modeling was then performed, involving well trajectory design, BHA design optimization, hydraulics modeling, and torque and drag modeling. The modeling included static simulation as well as drillstring vibrations using finite element analysis (FEA) dynamic simulation. This extended engineering analysis improved the bit and BHA selection capability. Several drill bits and BHA options were modeled and simulated under different drilling conditions to determine the most stable configuration. Simultaneously through the dynamics simulation, a stable drilling parameters plan was generated to improve the drilling performance. The modeling results indicated that the lighter BHA configuration minimized BHA - formation contact area, allowing for smoother and efficient weight transfer downhole. A reduction in BHA vibration produced a step improvement in ROP and drilling performance. The engineering modeling results were implemented by replacing the previously used motor BHA drill collars with heavy-weight drillpipe and smaller size jars. This hardware change resulted in an unprecedented cost reduction, a 52% improvement over the previous motor BHA in delivering the challenging section, achieving multiple additional records, and 56% ROP improvement over the field. This paper will present the design process and the detailed results for each run. Recommendations will be provided on how this process can be applied to increase ROP performance and reduce the cost per foot for such drilling applications.
Combination of well design practices, geo-steering with neutron-density and multilayer bed boundary mapping tools with a motorized rotary-steerable service (RSS) bottom-hole assembly (BHA) has been successfully used in the Ghawar field to accurately detect multiple formation layers enabling drilling performance improvement and optimized well placement services in challenging carbonate wells. The objective of the work-over program is to establish water-free gas production from the reservoir, especially as the gas-water contact (GWC) rises with on-going production. The Ghawar field is located in the eastern part of Saudi Arabia which contains non-associated gas in the target formation varying greatly in depth from the North and South of the field. The target formation consists of major gas bearing intervals, known as Carbonate Layer A and Carbonate Layer B. The Carbonate Layer-A averages about 120 ft in gross thickness and consists primarily of dolomite capped by anhydrite. The Carbonate Layer-B formation, like the Carbonate Layer-A, consists mainly of dolomites capped by tight anhydritic dolomites. In addition, these wells are drilled in the minimum horizontal stress directional for the advantages of optimized hydraulic fractures during stimulation phase and thus improved productivity. But these wells are notorious for stuck pipe risks, tripping difficulties and slow drilling penetration rates (ROP) with high shocks and vibrations. These risks are primarily due to geo-mechanical wellbore instability and uncertainty in both GWC depth and reservoir pressures arising from the strategy of drilling through multiple layers. With very low contrast in resistivity and the complex nature of the targeted reservoir, steering with only resistivity contrast using conventional bed boundary techniques would not suffice. Ideally, steering in a single layer of the target formation will eliminate the risks associated with the traditional steering method of passing multiple layers. Neutron-density combined with a new multilayer bed boundary mapping service were successfully deployed in deep gas Udhailiyah on four different wells. This service provided precise delineation of targeted reservoir layers in addition to giving an estimate of formation dip resulting in faster and more accurate geosteering. Steering effectively in these complex thinly bedded reservoir layers has shown improved drilling and tool reliability indicators, including incremental ROP improvement, zero stuck-pipe incidents, stick-slip and shock reduction, and the confidence to push with maximum parameters with a motorized RSS BHA to minimize open hole exposure and avoid borehole deterioration effects with time.
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