The hydraulic fracturing technology is widely applied in tight reservoirs, including shale reservoirs, as one of the established reservoir stimulation methodologies to enhance the productivity. Even though the hydraulic fracturing is currently a common technique, there are remaining challenges in offshore fields with the high degree of geological and geomechanical uncertainties. In offshore hydraulic fracturing operations, key issues are the limited deck space for the required equipment on-board and economical aspects of the surface equipment including stimulation vessels due to the limited number of dedicated offshore stimulation vessels in the world. In addition, the limited reservoir information brings uncertainties in the hydraulic fracture design and causes difficulties in finalizing the operation plans from the timing and logistics point of view.This paper contains the first part of the two successive parts of a case study will be shown on successful optimization and productivity enhancement of actual offshore hydraulic fracturing for a deep tight gas reservoir with considerably limited formation data and under a high-pressure and high-temperature (HP/HT) environment. This successful operation was recognized as a landmark in this region, in terms of the first hydraulic fracturing operation in the offshore Abu Dhabi.In this paper (part 1), we describe how the flexible hydraulic fracture design led to an efficient productivity enhancement. The hydraulic fracture design was optimized by the integrated data acquisition strategy and the successive flexible adjustment from the design stage at office to the actual main treatment at wellsite. The relevant fracture design components like proppant usage and size can be optimized, based on sensitivity studies assuming not only all possible geological and geomechanical circumstances but also the actual pre-frac well test and data-frac results. In part 2, the key factors will be highlighted on this successful hydraulic fracturing result against the difficulties from operational point of view (Al Ameri et al. 2014).The work flow and successful strategy in our hydraulic fracturing design and execution can be applied to other offshore tight-sand gas reservoirs including those under HP/HT condition. The optimized design of hydraulic fracturing provides an effective operation and enables more economical field development for the tight reservoirs.

Driving efficiency to ensure cost and risk reduction in well operations is paramount for any operating company; to achieve this, the main objective was to implement a continuous improvement process that measures performance to then improve it, acquiring lessons learned and finally implement new technologies to reduce non-productive time, invisible loss time and push the technical limit to the limit. The first step was to measure the current performance to determine average and best references to compare against. The drilling operations and engineering teams defined KPIs for each well type and respective sections and activities involving all levels of the organization including every individual, ensuring effective communication inclusive of Rig Crew and Service Providers. The initial KPIs were defined, discussed, validated and agreed by both operations and engineering management, all engineers were informed and challenged to measure their performance against KPIs. Once new records were achieved, a workflow to document best practices initiated, once identified, validated and documented, becoming the new standards. Similarly, once average performance was not achieved, a ‘Lessons Learned’ workflow was initiated. Aiming to get the team engaged a communication protocol of the Highlights and Lowlights was put in place, including recognition during operations meeting and emails. The primary results of the deployment of this initiative include the delivery of a 10% additional well count compared to the initial year's plan. An overall improvement of the overall Drilling and Completion Performance was also noted. An important improvement of the overall Rate of Penetration (ROP) was observed, as one of the key performance indicators. It was also notice a considerable reduction of the Flat time. New practices for losses mitigation in hazardous areas were stablished. The lower completion design was enhanced. The upper completion design and utilize Dual Hydraulic Packer in Oil producer well was optimized. Finally, the 1st Maximum Reservoir Contact Well was completed for two of the three Fields in the Team. The added value achieved by the implementation of these innovative practices includes the implementation of the KPI Gauges as a visual instrument to be used on daily operations meeting by the engineers and management, to quickly and effectively understand performance and improvement in multiple dimensions. Additionally, the implementation of a continuous improvement mind-set, focus in introducing changes gradually instead of radically to ensure a soft and solid adoption embraced by all team members. Finally, the improvement of the office-field communications, including a sense of ownership and achievement for each goal to achieve and record to break, to the point that every colleague involved in a specific operation, independently of their organization (Operator, Contractor or Service Company) is equally committed and engaged.

The first application of hydraulic fracturing in the offshore Abu Dhabi was executed safely and successfully. This achievement will be a valuable foothold to expand the field development target toward more challenging reservoirs such as deep tight sand in this region. There were huge amount of operational difficulties to carry out this hydraulic fracturing due to various operational restrictions, limited data availability and high-pressure & high-temperature (HP/HT) condition. Finally, these difficulties were successfully overcome by an intensive designing study on well completion, surface equipment, and operation associated with hydraulic fracturing for a tight gas reservoir.In this paper (Part 2), the key factors that led this trial to the first successful hydraulic fracturing in the offshore Abu Dhabi are described against the difficulties from operational point of view such as well completion design, arrangement of fracturing and surface testing equipment and acquired lessons learnt. However hydraulic fracturing design optimization from subsurface point of view is discussed in the other paper described by Kuroda, et al. (2014) as Part 1. Well completion design and equipment arrangement were optimized to overcome an extremely wide range of pressure and temperature condition with multi stage fracturing. Fracturing and testing equipment of high specification were arranged on the limited space of both the off-shore jack up rig and the fracturing vessel, and then these well-prepared equipment contributed to safe and accurate operation. Acquired lessons learnt will contribute to other offshore tight-sand gas reservoirs development in the offshore Abu Dhabi. These outcomes will be especially applicable in this region to optimize offshore hydraulic fracturing for tight HP/HT reservoirs in order to enhance the well productivity and enable economical development of marginal fields.

Hydraulic fracturing is an important technique widely used for to improve well productivity in tight reservoirs and enable economic development. Geomechanical modeling is an important prerequisite required to ensure effective fracture construction and the required contact with the formation. In this paper, we show the first successful hydraulic fracturing in the Offshore Abu Dhabi clastic sand formations in which geomechanical modeling played an essential role in fracture design, completion design and successful execution.The geomechanical properties and behavior of the clastic sand formations are still largely unknown in the Abu Dhabi region. In other parts of the Arabian Plate this formation is known to be a complex geological environment with high fracture gradients, poorly consolidated intervals, natural fractures and often rock that exhibits poroelastic behavior.Due to the aforementioned complex geological environment resulting geomechanical attributes, the fracture design and key inputs including the calibrated Mechanical Earth Model (MEM) were essential to the successful design and execution of the first hydraulic fracturing in the Offshore Abu Dhabi clastic sand formations. The lessons learned during this successful design and application is critical for the design of future wells and the development of the UAE clastic sand formations.The constructed MEM played a key role in successful hydraulic fracturing. Fracture height, length, width, direction, complexity and overall fracture performance are all largely controlled by the formation stresses, stress direction, rock properties and complexity of the rock fabric.Geomechanical properties in the clastic sand formations in Abu Dhabi offshore were evaluated with less uncertainty by utilizing the advanced MEM. The calibrated MEM was integrated with an advanced fracture design simulator to optimize hydraulic fracture design. Results of the advanced MEM agreed well with fracture diagnostics and temperature surveys.Work flow in this geomechanical analysis can be applied to hydraulic fracturing in other offshore tight reservoirs with a complex geological environment. Understanding the geomechanical properties of a formation allows engineers to optimize well placement, completion design, perforation placement, charge/gun selection and fracture design for improved well productivity.

In attempting to drill a deviated 12-1/4″ 37° tanget section with WBM through the Laffan and Nahr Umr shale intervals, very little margin for error was faced in a well where failure was not an option. While problems in the Nahr Umr were to be expected, the instability of the Fiqa and Laffan shale layers became the catalyst for excessive non-productive time. Two lost holes preceded the successful completion of the section after taking the last resort step of a re-drill with Synthetic Oil Based Mud (SOBM). Various literature is available on wellbore stability problems in the Nahr Umr Formation on a regional and field specific scale. Behaviour of the shale and how best to control it is also known to vary on a field by field basis. Failure mechanisms are largely related to the mineralogical composition of the shale itself in combination with the localized geomechanical forces exerted on the specific wellbore. This paper captures the specific experience encountered in the operator's first well in the country and provides insight into the severity of the risk of wellbore instability. Numerous operational issues were encountered due to shale instability induced through drilling and tripping related mechanical forces. Before committing to the changeover to SOBM, exhaustive attempts were made to find an acceptable and workable compromise to the challenges faced while drilling the section with WBM. This included implementation of alternative methods of well construction including the use of innovative tools and hole enlargement to increase annular clearances with the BHA. Often it was observed that mitigation of one problem led to the onset of another problem. The experience is used to present an overview of the limitations of the contingency options available and the impact of unplanned changes implemented during the well construction phase. In addition to the engineering conclusions presented, the case study provides insight into the complexities of a start-up drilling operation. Where an entire field appraisal campaign depends on the successful accomplishment of primary objectives, the necessity to perservere through adversity becomes of yet higher importance.