For many years, Saudi Aramco has searched for a way to replace the practice of drilling out the DV’s and Shoe Track with a tricone bit, followed by a polycrystalline diamond cutter (PDC) bit to drill the new formation to the next casing point. Many bit manufacturers have conducted trials to overcome the challenge, with limited success. This paper discusses a successful, single-run technology to drill out and continue drilling using only a PDC bit.
Investigations of the root causes of failure and erratic performance led to extensive review of bit design and drilling practices, but fail to overcome the single-run challenge posed by cutter wear and damage experienced during the drill out.
Recently developed shear cap technology provides a means of installing high-grade tungsten carbide caps on the PDC cutters. The caps protect the cutters during the drill out, and then wear away to expose the cutters in pristine condition for drilling the formation.
The shear cap technology has been tested extensively and optimized using various bottom-hole assemblies. The result has been a considerable breakthrough in the success rate for drilling the formation section, accompanied by a time reduction that has resulted in huge savings in offshore oil drilling operations.
The standard PDC bits fitted with the protective technology are successfully providing a one-trip capability, saving a round trip to change the bit and achieving a 100% success rate in drilling to the next the casing point. When drilling in the casing, the tungsten carbide shearing caps are effectively mitigating the cutter damage typically experienced when drilling out the shoe track. Drilling performance in the formation and the ability to efficiently drill the full section, demonstrates the undamaged condition of the cutters when the bit exits the casing. Overcoming the longstanding efficiency challenge of drilling both shoe track and formation in a single run is being achieved with the novel technology’s ability to enable optimal formation drilling by protecting cutters during the shoe drill out.
A truly optimized completion requires a wide range of understanding and activities. Starting with a thorough understanding of the reservoir, each completion element must be fully addressed from connecting to the reservoir, to enhancing the reservoir through proper treatments, to conducting hydrocarbons to surface for optimal efficiency. By considering the cause-and-effect interactions between these activities, each individual process can be designed and performed better, ultimately delivering the best overall solution. This overarching philosophy is also fully applicable to perforated completions.
Providing a perforating solution that is truly optimized for the reservoir is challenging, requiring advanced laboratory testing capabilities, reservoir specific products and systems, robust analysis and modeling tools, and a thorough process to insure solutions are designed, executed, and reviewed for continuous improvement and optimization. Recent advances in in-situ perforation testing techniques provide significant insights into dynamic events during perforating as well as enabling more reservoir specific equipment designs. Furthermore, state-of-the-art computational models complement testing methods by correlating dynamic perforating events and inflow analysis to actual productivity. Numeric modeling techniques also allow results from lab testing to be better translated into field scale environments. And finally, rigorous procedures can be followed to practice this process across a wide variety of completion types to provide well optimized perforated completions.
This study will detail the techniques used to employ the philosophy, and multiple case histories of such applications with results and lessons learned. In these cases, a comprehensive consideration of the overall completion was critical in optimizing the perforating process. The use of laboratory testing, customized products and systems, integrated modeling and analysis tools, and a disciplined process have led to the successful application of this scientifically engineered philosophy. This unique perforating philosophy is also aimed towards integration with other completion methods like hydraulic fracturing & stimulation, sand control and management and above all, enhancing reservoir productivity.
Reddy, S. S. (Oil and Natural Gas Ltd) | Anjaneyulu, J. V. (Oil and Natural Gas Ltd) | Lal, Abhay Kumar (Oil and Natural Gas Ltd) | Rao, E. J. (Oil and Natural Gas Ltd) | C H, Ramakrishna (Oil and Natural Gas Ltd) | Talreja, Rahul (Schlumberger) | Bahuguna, Somesh (Schlumberger) | Zacharia, Joseph (Schlumberger) | Chatterjee, Chandreyi (Schlumberger) | Basu, Jayanta (Schlumberger)
Malleswaram field in Krishna-Godavari (KG) basin has proven gas reserves in the late Cretaceous Nandigama formation. Many drilling challenges were faced, including losses, tight hole, and stuck pipe in the Raghavapuram and Nandigama formations overlying the reservoir interval. This study was conducted to provide a solution for drilling optimization by mitigating drilling-related nonproductive time (NPT). Integration of acoustic and geochemical data for geomechanics study provided a new insight into cause of overpressure and need for revamping of casing policy to significantly improve wellbore stability, mitigate risks, and ensure future drilling success. Generated stress models can be used to optimize hydraulic fracturing in these reservoirs. A completion quality based on stress model indicates the need for multistage fracturing due to the presence of stress barriers inside sand units in Nandigama formation.
Underbalanced drilling technology is widely used to minimize formation damage in the reservoir section and enhance productivity. It involves drilling with a fluid whose hydrostatic pressure is lower than that of the formation being drilled. As a consequence of this lower hydrostatic there is a continuous flow of hydrocarbons to surface which is handled by separation equipment and exported thru pipelines where they exist or burned at the flare if no transportation infrastructure is located near rig-site.
The injection of nitrogen into drill-pipe to lighten the hydrostatic pressure of the drilling fluid introduces significant challenges with regards to corrosion mitigation planning. A very well developed corrosion mitigation plan often exists for single phase drilling fluid but the introduction of a gaseous phase leads to changes that need to be incorporated to prevent against excessive corrosion.
Problems and complications due to corrosion issues were hindering an underbalance drilling operation's progress. This paper examines how, optimizing the corrosion control techniques leads to improved drilling performance in subsequent bit runs. The willingness by the operator to tweak and improve the chemical concentrations and learn and apply those lessons learned immediately in the field pays immediate dividends.
Al-Ansari, Adel (Saudi Aramco) | Parra, Carlos (Saudi Aramco) | Abahussain, Abdullah (Saudi Aramco) | Abuhamed, Amr M. (Saudi Aramco) | Pino, Rafael (Saudi Aramco) | El Bialy, Moustafa (Halliburton) | Mohamed, HadjSadok (Halliburton) | Lopez, Carlos (Halliburton)
A properly designed reservoir drilling fluid and precise control of its properties are essential to prevent formation damage issues that hamper production. An essential prerequisite for a reservoir drilling fluid are nondamaging specialty products and reduced fines and fluids invasion. This paper describes the case history of two deep gas wells in Saudi Arabia, one well showed impaired production due to screens plugging and was put on workover drilling operations whereas the other well was a regular development well. The offset data showed differential sticking, partial losses and tight spots while drilling the 8⅜ and 5⅞ in. hole sections.
The well reservoir data including the bottom hole-temperature – 300°F, permeability – roughly 10 to 20 micron pore throats and lithology – sandstone intercalated with shale, for the reservoir section were determined from offset analysis. Extensive lab testing was performed with nondamaging specialty and optimized PSD for minimized fine and fluids invasion. This engineered fluid was used to drill a 5⅞ in. vertical side track of ± 300 ft for the workover well whereas on the regular development well about ± 400 ft of the 5⅞ in. section was drilled. The fluid was continuously monitored for PSD at the rig along with the particle plugging test for fluid loss control. The hole cleaning and equivalent circulating density was monitored and programmed with a proprietary hydraulics software. All the fluid properties were determined to be within planned range. The wells were drilled without any of the offset problems as discussed above followed by running the 41/2 in. conventional sand screens to the bottom without any issue. Initial flowback production testing was performed on the workover well, which took 8 hours as compared to the usual 48 hours in the offset wells. The BS&W (basic sediment and water) from day 1 of production was 9% as compared to the 25% observed in the offset wells. The gas production rate was 200% more than was expected as per the offset information.
This paper shows the successful use of reservoir drill-in fluid on two gas wells: one was a workover well and another a regular well. The abstract presents a mutual approach between Halliburton and Saudi Aramco to address the issue of minimizing formation damage and mitigating differential sticking. Offset well data learnings, optimized PSD design, monitoring at the rig site, and the use of nondamaging specialty products delivered production optimization.
In Kuwait, the traditional approach to Field Development has been to drill wells, whether Vertical or Horizontal, Single or Dual, with completions dedicated to either Production or Injection. However, as increasingly more wells are being drilled to develop the stacked reservoirs, surface infrastructure is growing in complexity with regard to Production Flowline routing, Gathering Facility location, Satellite Manifold placement, Water Injection distribution lines routing, and access road construction. Also, since the reservoir stack is a combination of areally extensive Carbonates overlying shale & channel sand sequences, optimum surface locations of Injectors for one reservoir is now increasingly conflicting with the optimum surface locations for the Producer of another reservoir.
The North Kuwait team presented options that could reduce the requirement for excessive wellbores for both new Producers and Injectors. One of which is the utilization of a single wellbore to both Produce Oil from one reservoir and Inject Water into another reservoir simultaneously. This novel approach utilized the most popular Dual Completion equipment, but rather than produce or inject concurrently from separate reservoirs or layers, production & injection are achieved simultaneously through either tubing string. Tubing movement calculations were made to ensure that the resultant axial tubing forces exerted by simultaneously injecting cold water and producing hot reservoir fluid would not cause the Dual packer to prematurely unset.
This unique completion has several advantages which include the production acceleration from an adjacent reservoir/layer that would have been postponed for the life of the Injector and the elimination of the drilling of a new producer to access the oil from an adjacent reservoir/layer to the target injection zone. Additionally, the elimination of the drilling of an Injector well if its optimum subsurface location is close to, or coincides with, an existing Producer from an adjacent layer, and the reduction in access road construction and location preparation costs. This strategy will significantly reduce Unit Development Costs while concurrently ramping up production levels. With simple conversion workovers, rather than drilling new wells, Oil Production potential that is presently unexploited in dedicated Injector wells can immediately be realized. Pressure support Injection can be initiated as soon as distribution injection lines are made available via similar conversion workovers.
Al-Houti, Naser (Kuwait Oil Company) | Al-Othman, Mohammad (Kuwait Oil Company) | Al-Qassar, Khalid (Kuwait Oil Company) | Al-Ebrahim, Ahmed (Kuwait Oil Company) | Matar, Khaled (Halliburton) | Al Hamad, Abdulla (Halliburton)
This paper presents the application of a unique gelling system for perforation shut-off operations that can help reduce operational time by 50% and can also be used as an effective water- and gas-migration control agent. The system combines a conformance sealant (based on an organically crosslinked polymer) with non-cementious particulates. The particulates provide leak-off control, which leads to shallow matrix penetration of the sealant. The filtrate from the leakoff is thermally activated and, as a result, forms a three-dimensional (3-D) gel structure that effectively seals the targeted interval after exposure to the bottomhole temperature (BHT).
The traditional method for recompleting wells into newer layers, after the current producing zones have reached their economic limit, involves several steps. The first step is to squeeze off the existing unwanted perforations using cement, drill out the cement across the perforations, and then pressure test the squeezed zones to help ensure an effective perforation seal has been achieved. The new zones are then perforated and completed for production. The entire operation can require four or more days of rig time, depending on the success of the cement squeeze. In cases of cement failure, the required time can extend to over one week. Common challenges associated with cement-squeeze operations include leaky perforations, fluid migration (gas or liquid) behind the pipe, or compromises in the completion. Attempts to remediate these issues must be repeated until all objectives are met.
The new perforation plugging system can be bullheaded into the well (spotted at a desired location in the wellbore), allowing for easy placement and calculation of the treatment volume. The limited and controlled leakoff into the matrix during the squeeze results in a controlled depth of invasion, which allows for future re-perforation of hydrocarbon-producing zones. The system can be easily washed out of the wellbore, unlike cement, which must be drilled out. The temperature range of the particle-gel system is 60 to 350°F, which makes it versatile.
To date, more than 500 operations have been performed with this system globally. This paper presents the results obtained from laboratory evaluations, the methodology of the treatment designs, and four case histories from Kuwait. A salient case is the successful use of the sealant/particulate system, resulting in shutting off all perforations after six failed cement-squeeze operations.
The prospect of reducing the required time to perform remedial cement-squeeze operations by 50%, as well as the ability to repair casing leaks and seal off thief zones, make this sealant/particulate system a valuable alternative to standard cement-squeeze operations.
Achieving effective fluid coverage of stimulation operations in deepwater frac-pack completions is often challenging due to a variety of factors, including, but not limited to, the length of screened intervals, the uncertainty of damage mechanisms, and the ability of diversion materials/fluids to divert beyond the screens and into the formation. This case study demonstrates a successful technique used in conditions not previously attempted.
This treatment in a deepwater, frac-packed well with fiber-optic-equipped coiled tubing (CT) and a rotating, hydraulic high-pressure jetting tool achieved the successful stimulation of a 500-ft-long frac-packed zone after several previous failures using different techniques. By using a CT equipped with fiber optics and downhole measurement tools, engineers were able to perform a data-driven operation based on real-time bottomhole measurements and distributed temperature surveys.
This successful treatment improved productivity by 75% compared to the well before treatment. Typically, treatments of this nature are investigated and techniques for a field or region are refined over the course of multiple stimulation operations of large numbers of similar wells in the area. However, in deep water, most fields have only a very small number of wells. The costs associated with gaining wellbore access to conduct an acid treatment and with handling produced stimulation fluids are very large compared with costs in other geographic areas. Each individual well has a high productivity, and improper stimulation is an enormously costly lost opportunity for the operator. This makes it very important to ensure that every job is performed as optimally as possible, without resort to iterative or empirical methods. This method increases the opportunity to produce a successful treatment the first time and expands the technical envelope of application. These enhancements should allow other operations of this type to be conducted that previously would have been too high risk to consider.
This was a high-pressure application compared to previous operations. It was one of the longest fiber optic cables injected into a CT reel. Modifications were made to the CT reel to support the expanded weight. A stronger type of fiber optic carrier had to be utilized. A customized testing and validation procedure had to be used to extend the operating envelope of the fiber-optic-enabled downhole tools to perform reliably.
The ability to drill wells in high temperature formations is limited by the temperature specification of the available drilling tools. Most drilling tools currently have a temperature rating of 150°C, and there is an ongoing effort to develop tools with a higher temperature rating. A parallel effort is to develop the modeling capability to simulate the complex downhole temperature environment, to allow engineer to understand the temperature effect on drilling operation and better manage the temperature-related risks.
Many high temperature wells are planned in an extremely conservative manner. The engineer will rely on the formation temperature measured in offset wells to determine temperature gradient of the planned well. This temperature gradient will be used as a reference for all aspects of the well design, including drilling tools selection, cementing design, etc. In reality, there are many factors which affect the actual downhole temperature experienced by the tools. There is a complex interaction between heating from the formation, drilling fluid circulation, and the mechanical action of drilling tools. There are many forms of energy loss contributing to the downhole temperature, such as mechanical friction, rock cutting, and fluid friction.
A new state-of-the-art dynamic temperature model is developed to simulate downhole conditions in order to precisely predict downhole temperatures. This paper will explain the development of dynamic temperature modeling and how the model being used to plan high temperature well. The paper will also present several case studies where the modeling was used on planning high temperature well and comparison between model results and actual downhole temperature measurements.
Calcium sulfate is inherently a difficult mineral scale during oil and gas production process because the amount of scale formed is much greater than that of barium sulfate at similar scale saturation index level, and it is very difficult to clean up. This is especially challenging in conjunction with HTHP stimulation treatments where compatibility of the scale control chemical with fracturing fluids is critical, and when longer-term inhibition performance is desired. A new solid inhibitor was developed for this purpose and applied in multiple wells in the Krishna Godavari (KG) basin offshore India to combat mineral scale within the proppant pack and production tubing over the long term, under extreme downhole conditions (T= 400°F, P=13,500 psi). Normally, downhole chemical injection mandrels and surface treatments cannot adequately control scale deposition under these conditions.
The new solid inhibitor product was made by adsorbing scale inhibitor onto a high-strength, proppant-sized substrate with a large surface area. The high-strength substrate were prepared by sol-gel chemistry through hydrolysis of aluminum alkoxides and formation of particles that are calcined and then sintered at high temperatures to produce a substrate with the desired strength and surface area. The scale inhibitor used exhibited excellent inhibition performance and good compatibility with metal based cross-linked fracturing fluid systems at high temperature.
Tests performed with proppants/substrates show that using high loading of the substrates with the proppant does not damage the proppant pack even under very high stresses, For example, API crush tests of a mixture of 80% conventional untra-high strength proppant with 20% substrate by weight at 13,000 psi produced less than 4.7% fines and 88% of the produced fines were larger than 100 mesh and the fracture conductivity of the pack is maintained. The results of comprehensive laboratory testing show the new solid inhibitor can prevent anhydrite scale up to 400°F, and is completely compatible with zirconium- crosslinked fracturing fluid at 350°F and above. To date, six fracture treatments have been performed using a total 23,800 lbs of this new solid inhibitor. The wellhead water samples are being collected for scale inhibitor residuals analysis, as the wells start to produce water.
To ensure compatibility of the inhibitors with high-temperature fracturing fluids, especially metal based cross-linked fracturing fluids, without compromising the inhibition longevity at high pressure and temperature remains a stiff challenge, although adding scale inhibitors to a fracturing fluid has been a well-established practice to provide long-term inhibitor protection during hydrocarbon production. The new approach described here meets this objective, extending the long-term well performance under HTHP conditions.