High torque, friction factors, and pick up weights were major challenges encountered by a major operator in Abu Dhabi while planning to drill challenging extended reach development (ERD) wells with complex 3D profiles. Well torque and drag simulations showed that planned depths were not reachable with water-based muds. This paper describes the implementation of a mechanical lubricant, which resulted in significant decrease of the friction factors and turned an ERD well from not drillable to drillable with water-based mud. After analyzing several possibilities, the solutions were narrowed down to two: use either a new generation mechanical lubricant or a reservoir non-aqueous fluid (NAF). The complexity was amplified by the necessity to re-design a filter-cake breaker for NAF, were this option to be selected, due to the type of completion. This second option would also create a substantial cost increase for the operator for products and rig time; therefore, the decision was made to introduce a mechanical lubricant. A comprehensive study and lab tests were conducted to ensure compatibility and stability of the lubricant with a planned mud type at downhole conditions. The results of this study were promising enough for the operator to introduce this lubricant, aiming a substantial reduction in torque and drag to enable drilling of the longest horizontal section in the history of the project. Before addition of the mechanical lubricant, drilling continued with a conventional type of lubricant, noticing an increasing tendency of torque and drag tracking the predicted trends. At a certain stage, drillstring buckling was observed and drillpipe started to reach their limits. To mitigate these impediments, the mechanical lubricant was introduced into the drilling fluid. After reaching the optimum concentration, the mechanical lubricant eliminated buckling and provided significant reduction in torque, pick-up, and slack-off friction factors, respectively by 27%, 52%, and 42%. These parameter improvements facilitated continued drilling the well to final depth without reaching the drillpipe limits. Additionally, the well and bottomhole assembly (BHA) designs allowed for significant margins in case of a stuck pipe event, and based on the new friction factors, the well could be extended by 3,000 ft without reaching the drillpipe limits. The impact of this exercise in future ERD wells is considerable. It will simplify well and completion designs, improve logistics by reducing the amount of chemical movements, facilitate drilling fluids selection, and optimize the well cost. The paper covers the gaps related to drilling complex ERD wells with water-based drilling fluids. It provides detailed methods and procedures covering the suitable application of the mechanical lubricant and the extensive laboratory tests done during the planning stage, as well as the field application and results. The proposed solution can be used during the well planning process in any other area of the world.
Horizontal wells enable drainage from a longer wellbore which helps to allow lower drawdown rate compared to vertical wells, minimizing gas or water coning. However productivity can be seriously affected unless mud cake damage is efficiently removed from all producing intervals along the horizontal wellbore. In recent years eco-friendly and non-corrosive bioenzymes (α/β-amylase) have shown great potential in cleaning wellbores uniformly and achieving higher well productivity. However in a low pressure fractured reservoir, there is always a possibility of localized reaction and loss of the clean-up fluid, unless the reactivity of the fluid is engineered based on the given well parameters. In this study α-amylase enzyme is modified to withstand higher thermal shock by structurally reinforcing the β-Helix layer to strengthen the catalytic centre by preferential protein hydration technique. Buffering was done to maintain different system pH and kinetic rate constant is derived through reducing sugar release measurement by DNS method using starch-xanthan gum-CaCO3 based drill-in-fluid as substrate. Though the overall reaction is extremely complex, a good correlation could be drawn between system pH and the rate of breaking mud cake into simple sugar. The kinetic rate constant index is used in final formulation of enzymatic clean up fluid for application in high temperature (110 °C) long horizontal wells drilled in carbonate formation, which allowed different soaking time due to operational constraints. The results show that there is excellent correlation between laboratory prediction and clean up efficiency in terms of well productivity.The study showed that each individual well demands a specific formula for clean-up fluid and higher than prognosed production could be achieved through custom formulation, based on well condition and operational requirement.
Injection of drilling waste into subsurface formations proves to be an environmentally-friendly and cost-effective waste management method that complies with zero discharge requirements. It has now become the technology of choice in offshore Abu Dhabi. The aim of cuttings reinjection (CRI) is to mitigate risks associated with subsurface waste injection and reduce cuttings processing time and cost. In order to meet these goals, a cuttings reinjection subsurface assurance methodology was developed to improve cuttings processing and continuously monitor drilling waste injection operations. Preparing for CRI operations required extensive drilling cuttings slurry testing to minimize processing time and develop optimum particle size distribution to reduce cost and increase the injected waste volume. The improvements were accompanied by downhole pressure and temperature monitoring of the injection well, thus facilitating analysis of injection pressures. Fracture containment was verified through a combination of pressure decline analysis, periodic injectivity test, temperature survey, and periodic modelling for fracture waste domain mapping. A backup injection well was used also as an observation well to monitor the pressure signitures in the injection formation. More than 1 million barrels of drill cuttings and associated drilling waste have been safely and successfully disposed of into a single injection zone of CRI well over three years of operations. The cuttings reinjection subsurface assurance method optimizes grinded cuttings particle size distribution, detects and identifies potential risks to provide mitigation options to prolong the life of the injector. The proactive subsurface injection monitoring-assurance program was built into the fit for purpose CRI injection procedure to continually avoid injecting any rejected hard material, improve and update the process as per subsurface injection pressure responses, thus reducing processing time and cost, mitigating injection risks, and extending the injection well life. This paper presents the unique and technically challenging cuttings slurry properties design and pressure interpretation experience learned in this project; the enhancement of cuttings processing helped increase injection volumes and an in-depth interpretation of fracture behavior which behaved like a risk-prevention tool with mitigation options. Significant enhancement was developed in slurry treatment procedures to avoid injectivity loss and maximize the disposal capacity.
It is common to be faced with severe losses prior to cementing the 9 5-8 in. intermediate casing in an offshore field in UAE. Intermediate casing covers weak zones and as a results there is always a high risk of formation breakdown and induced losses while running the casing and before it reaches intended setting point. The average losses experienced during drilling the 12 1-4 in. hole may exceed 100 BPH. The main challenge in the case reviewed in this paper was that the formation was fracturing during casing running, compromising ability to achieve proper zonal isolation and successful cement job execution. To address the challenge a special LCM Spacer system was proposed, designed to minimize or eliminate the losses during the primary cement job by offering superior sealing capabilities. This LCM Spacer system can easily mitigate loss circulation while cementing, based on ultra-low invasion technology forming a barrier across loss zones. It creates a film across formation walls and reduces the loss circulation ranging from partial to total losses on permeable, fragile, weak formation, natural fractures and depleted reservoirs. It also improves wellbore stability and ECD’s along the wellbore and expected loss zones. The LCM Spacer system was designed and implemented based on the well conditions, design guidelines and previously recorded global success of the system applied in similar applications.
Good cementing practices are required to achieve effective zonal isolation and provide long-term well integrity for uninterrupted safe production and subsequent abandonment. Zonal isolation can be attained by paying close attention to optimizing the drilling parameters, hole cleaning, fluid design, cement placement, and monitoring. In challenging extended reach wells in the UAE, different methods were employed to deliver progressive improvement in zonal isolation. Cementing the intermediate and production sections in the UAE field is challenging because of the highly deviated, long, open holes; use of nonaqueous fluids (NAFs); and the persistent problem of lost circulation. Compounding the problem are the multiple potential reservoirs; the pressure testing of the casing at high pressures after cement is set; and the change in downhole pressures and temperatures during production phases, which results in additional stresses. Hence, the mechanical properties for cement systems must be customized to withstand the downhole stresses. The requirement of spacer fluids with nonaqueous compatible properties adds complexity. Lessons learned from prior operations were applied sequentially to produce fit-for-purpose solutions in the UAE field. Standard cement practices were taken as a starting point, and subsequent changes were introduced to overcome specific challenges. These challenges included deeper 12 ¼-in. sections, which made it difficult to manage equivalent circulating densities (ECDs), and a stricter requirement of zonal isolation across sublayers in addition to required top of cement at surface. To satisfy these requirements, several measures were taken gradually: applying engineered trimodal blend systems to remain under ECD limits; pumping a lower-viscosity fluid ahead of the spacer; using NAF-compatible spacers for effective mud removal; employing flexible cement systems to withstand downhole stresses; and modeling the cement job with an advanced cement placement software to simulate displacement rates, bottomhole circulating temperatures, centralizer placement, mud removal and comply with a zero discharge policy that restricts the extra slurry volume to reach surface. To enhance conventional chemistry-based mud cleaning, an engineered scrubbing additive was included in the spacers with a microemulsion-based surfactant. The results of cement jobs were analyzed by playback in advanced evaluation software to verify the efficiency of the applied solutions. This continuous improvement response to changes in well design has resulted in a significant positive change in cement bond logs; a flexural attenuation measurement tool has been used to evaluate the lightweight slurry quality behind the casing, which has helped in enhancing the confidence level in well integrity in these challenging wells. The results highlight the benefit of developing engineering solutions that can be adapted to respond to radical changes in conditions or requirements.
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