TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSeveral methods of cleaning deviated and horizontal wells have been developed over the years. One of the most common methods is running in with coiled tubing and circulating the solids out with a liquid or multiphase fluid. Solids tend to settle at the bottom or low side of the wellbore in highly deviated or horizontal wells. This makes the cleanout process inefficient in bringing the solids to the surface. In this field, most of wells are horizontal. One of matured fields in the northern directorate of Petroleum Development Oman manily produces from horizontal wells. The produced water is injected back into the reservoir. Scale is found in injectors and producers. The acid insoluble materials in these scales vary from 4% to 22%. Hence, cleanout of the horizontal hole is required in this field to keep the wells producing/injecting at their potentials. Various methods of cleaning like coiled tubing cleanout and reverse circulation through workstring during hoist/rig operations were tried in cleaning the horizontal wells. However, they were not successful in cleaning the horizontal hole. One of the main reasons is the loss of kill/completion fluid into the formation during well operations. In order to establish an effective cleaning method in this environment, it was decided to experiment the coiled tubing reverse circulation process in cleaning horizontal openhole injectors so that the same process could be extended for cleaning out horizontal producers.

There are number of challenges encountered in oil production of mature, depleted fields like naturally fractured complex carbonate reservoirs found in Oman and the Middle East Region. These include production under high water cut ranging from 90 to 99%, the presence of conductive natural fractures connected to the aquifer in the producing zones, multi-zone production and reservoir heterogeneities encountered in each zone. Conventional acid stimulation at such reservoir conditions is rather questionable, showing no economic value and exhibits very high risk of losing the remaining oil production with unwanted, further increased water production. However, acid stimulation combined with water control gives good opportunity for recovering extra oil using hydrophobic chains containing associative polymer. The polymer adsorption has double roles during and after the treatments acting as an acid diverter and water control agent as relative permeability modifier. In naturally fractured producing zones, this combined method shows lower risk and better potential than in those zones where matrix flow exists only. In summary, this paper will cover the theory behind the above-mentioned method, stimulation challenges, candidate selection, treatment design and the results of the campaign started since 2006 in one of matured fields in North Oman. The campaign focused on oil producing wells having more than 97 % water cut. These trials were the last chance for achieving acceptable oil production before abandonment. The main achievement of the campaign resulted in more than 207% incremental oil (net) added to the stock tank in parallel with 1.5% average water cut reduction. The technology will be applied in a bigger scale as part of production optimization.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper details the challenges of stimulation in one of the fields in North Oman. The field is a mature, heavily faulted and fractured carbonate reservoir on water flood where acid stimulation carries an inherently high risk of inducing several fold increases in water production. Acid placement challenges are immense as the fracture networks impart massive permeability contrasts and are most often the principal conduits for "premature" injection water breakthrough. We present field data of acid stimulation treatments on cased hole, oil producers as well as open-hole horizontal injectors using a novel self-diverting acid system. This fluid has been recently applied in other reservoirs but to date, none of these applications have held the same magnitude of challenges and barriers to successful implementation of stimulation treatments. We present numerous field studies which identify self-diverting acid systems as a key solution, together with best practices in candidate selection (through reservoir logging evaluation) and coiled tubing placement methodology, in providing consistent improvement in net hydrocarbon well productivity and enhanced injection profile for reservoir management. In addition we present results of a new surfactant based self-diverting system and compare the results to conventional polymer based treatments in this field. The results are indicative of a further improvement in success ratio of acidizing treatments. Similar methodology and fluid systems are applicable in other complex fractured reservoirs where acid placement and minimizing water production present the principal challenges. Moreover, as reservoir management becomes an ever-increasing concern, we present a treatment methodology to enhance productivity, reduce water cut and optimise reservoir sweep, all of which reduce the overall lifting costs.

A failed Electrical Submersible Pump (ESP) well is generally identified when there is no flow to the surface. The process of reviving well production can take weeks leading to huge unwanted deferment. Through a Proof-Of-Concept (PoC), the objective is to prototype and evaluate the results of an early failure detection for ESP wells using Machine Learning (ML), without reserving focus on implementation. By demonstrating the feasibility of this approach and verifying that the concept has practical potential, the tool can be used to reduce deferment and identify failure prone component to either devise mitigation strategy for extending time-to-failure or work on an improved design before failure. The paper details all the work undertaken to develop a Predictive Analytics model based on ML algorithms using field sensor data, real time physics-based model calculated data and well failure history to predict ESP well failure and identify failed component in advance. The approach of database standardization, data pre-processing, machine-learning algorithm selection, supervised training and validation dataset creation shall be discussed. ESP domain knowledge used for Feature Engineering across multiple modeling iterations to consistently improve well and component level model metrics shall be detailed. After the evaluation by well owners at Petroleum Development Oman (PDO), refered as Operator's blind test, the prediction of the ML algorithm shows a good accuracy in its ability to capture historical failures ranging between days to months in advance. The Well Level Failure model captures failure prone wells with a precision of 90% and accuracy of 76%. The Component Level Failure model correctly identifies pump failure from other failures with a precision of 92% and accuracy of 88%. These numbers show the reliability of future predictions that could enable users to make high stake workover and operating envelope optimization decisions with confidence. Following benefits are estimated from both Well failure and Pump Component failure prediction models metrics respectively: 28.35% savings from total unscheduled ESP deferment1% increase in Overall Mean Time to Failure (MTTF) based on optimization of predicted pump component failure wells. In an organization where over thousand ESP wells are managed by limited production engineers, post ESP failure, the effort invested for hoist scheduling, raising new well proposal, rig mobilization, new ESP installation and commissioning utilizes huge time and leads to long undesired oil deferment. Implementation of engineered analytics to predict ESP failures and failed components in advance can support production engineers to plan early for workover operations, increase well run life and minimize oil deferment losses. Methodologically assessed by Senior Petroleum Engineers in selected clusters (using historical data and in the context of each failure and non-failure cases), the Predictive Analytics journey has started. It is ready to be operationalized at a small scale to build confidence as an advisory tool for Production Engineers in real-time to evaluate multiple wells’ failure probability on a daily basis and generate massive savings from well deferment. This agile journey focused on value generation is achieved with combined efforts between technology, domain knowledge and data.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes new methods to economically improve production levels in one of the mature fields of Petroleum Development Oman. This field had been developed by infill drilling programs, which were suspended in early 2001 to review the development strategy. A reservoir management team set a challenge to effectively conduct logging operations and quickly utilize the data collected to identify and avail of optimization opportunities, thus maximizing the production of the wells whilst lowering overall costs. The optimization activity consisted of clean-out, saturation logging, perforation and stimulation. These activities were carried out either with coiled tubing only utilizing conventional practises and e-line coiled tubing, or with the combination of coiled tubing and hoist through multiple well entries. Both of these methods were successfull in that they resulted in incremental net oil production but at relatively high costs. This paper presents a methodology which enables clean-out, logging, stimulation and perforation with one coiled tubing intervention, which includes a plastic coated "e-line" coiled tubing, coiled tubing perforating head and new perforation technology. All systems are in complete compliance with the most stringent safety criteria. The new method has a considerable time and cost savings impact, and this is fully illustrated in this paper with field trial case histories, in which a multi-disciplinary team effectively targeted the most suitable zones for perforation and stimulation using a state of the art self diverting, non damaging, acid system. Technical and economic comparisons are made with conventional practices. The methodology is currently being employed in this field and is potentially applicable to other fields.