In current depressed oilfield industry environment, economical and operational effectiveness becomes even more important especially in complicated, challenging projects that demand large investments and simultaneous utilization of multiple technical services. In Petroleum Development Oman (PDO), there are a few gas fields having similar downhole conditions with multiple target pay zones, whereas fracturing operations are complicated by the requirement of CT cleanouts and/or milling in between the stages. Multizonal and multistage frac operations are commonplace in oil and gas reserves around the globe, however despite of increased number of wells stimulated using specialist multistage completion equipment, the most often utilized completion design for this operation is still plug and perf, especially in vertical wells. There are also techniques on the market involving coiled tubing for perforation and isolation between the stages, however they have their own constraints and limitations, especially in high-pressure and high-temperature environment. For PDO wells, multistage completion technologies were not feasible, therefore conventional plug & perf approach had been selected as the optimum option. The main drivers behind this selection are the challenges associated with precise deployment of the completion jewellery across small pay zones and limited coverage of the target zones when using frac sleeves. Another constraint in the past was the pressure rating of the multistage completion systems existed on the market. Plug and perf completions are designed to allow pinpoint placement of isolation and reservoir access with on the fly adjustability. This means that there is more freedom in selecting desired perforation interval, plug-setting depth and no additional restrictions on the pumping rates that are incurred by CT string inside the tubing as in some of the popular techniques. The zonal isolation is the portion of the design that allows the frac treatment to address the target intervals without affecting the others. In operations requiring 15k+ differential pressure ratings, isolation becomes extremely challenging and requires robust and reliable technology to ensure true integrity so stimulations can be placed as per design. This challenge may get even worse with increasing temperatures, whereas conventional composite compounds are not applicable due to "swelling", or getting softer. The primary job of the frac plug is to isolate but operational safety and millability also must be taken into consideration for the overall efficiency of a completion design. Additional challenges in the target fields are the depletion of the zones and their extreme breakdown pressures that are not only exposing frac plugs to extreme differential stresses but also causing difficulties during milling operations, whereas maintaining balanced circulation becomes a primary task in order to prevent coiled tubing differentially or mechanically sticking in the wellbore. That is adding another requirement for the frac plugs - be easily millable and produce as small cuttings as possible to improve debris removal. The high pressures, high temperatures, aggressive fluids and long exposure time seen by isolation plugs in these frac operations had been a challenge for current treatment and completion designs due to availability (and reliability) of equipment and tools represented on the market, therefore Petroleum Development Oman and the frac service provider collaborated to engineer a successful solution. It involved multiple steps, such as development of the specific design requirements, integrity-testing criteria and field trials before the plug could be adopted for wide application. The target design was a plug with a ~3.45" maximum OD, having true 15k+ differential rating at ~400F+. This composite/metallic hybrid plug was supposed to be able to withstand the harsh downhole environment seen in the various PDO fields in Oman land operations and resolve multiple complications associated with well interventions in these fields.

Hydraulically fracturing operations is becoming much more complex as the gas formations are being depleted with the time. In addition to this, some gas reserves need to be recovered by fracturing horizontal wells with multiple stages which is the case of an extensive gas field in the Sultanate of Oman that has been producing since 1991 mainly by hydraulic fracturing. The scope of this paper is to discuss the different methodologies in the operations associated to hydraulic fracturing in horizontal gas wells with formations depleted in PDO, the main objective is to show operations and well delivery improvement by the optimization of tools conveyance, perforating techniques, clean out and milling strategy. The paper will show the enhancement of the operations and the outstanding results in these challenging well conditions. The paper will start by describing the different methods used to execute operations for fracturing horizontal wells which are mainly related to plug and perf technique, clean out and milling plugs in between stages. Further, it will discuss the strategy, planning and job execution of one of the wells with 14 stages in the horizontal section, the perforating technique and strategy used to help reduce screen out's, it will also discuss the acquisition of spectral Noise log data post fracturing with the assistance of Nitrogen as well as the milling of the isolation plugs at the end of the job. The optimization of the conventional operations is a novel approach to enhance hydraulic fracturing in depleted horizontal gas wells in PDO, this is in alignment with the continuous improvement ideas and the lean thinking across the oil and gas industry. It is easy to replicate in other horizontal wells to be hydraulically fractured which will reduce cost, HSE exposure and will help increase the recovery of hydrocarbon reserves.

Recent years and especially the coronavirus pandemic have been very challenging for the oil industry, resulting in a significant reduction in investment, forcing companies to review budgets and search for more efficient and economical technologies to achieve the target level of hydrocarbon production and revenue generation. In PDO, one of the most challenging fields is "AS", where extreme downhole conditions require a very well-engineered approach to become economical. This field has already seen some of the most advanced technology trials in PDO that are also covered in multiple SPE papers. Based on the new approaches and techniques that were successfully implemented on recently drilled wells, it was decided to review the older, previously fractured wells in the area and assess them for a refracturing opportunity. The main challenge in this project was that these older wells were previously hydraulically fractured in multiple target intervals, therefore both zonal isolation and successful placement of the new fracs were becoming the major concerns. As the planned coverage by the new fractures was to ensure no bypassed pay, the only applicable technology on the market was a pinpoint fracturing process, whereby the targeted placement is achieved through limited entry perforations and focused energy of the injected fluid. The subject pinpoint technology anticipates that the limited entry sandblasting perforation is created and then proppant laden fluid is pumped through a sandblasting nozzle which is part of either a coiled tubing (CT) or a jointed pipe (JP) Bottom Hole Assembly (BHA), and the backside (or the annulus of the injection path) is used to maintain the positive backpressure from the top. This technology allows for choosing a desirable order of target interval selection inside the well, unlike conventional plug and perf or a simplified multistage completion, where the treatments must be placed only in order from bottom to top. Another advantage of this approach is a faster frac cycle through the elimination of wellbore cleanout requirement. Being a unique and first-ever application in the Middle East, using CT for placing frac treatments through a jetting nozzle demonstrates the full scale potential of this approach not only in conventional wells but also in complex, sour and High Pressure (HP) environments that are often found in the Sultanate of Oman and in the Middle East. This paper will cover the advantages and disadvantages, complexity and requirements, opportunities and lessons learnt in relation to this approach.

Post frac cleanout and milling operations are considered some of the most critical activities that leverage on the operational benefits of coiled tubing. Therefore, they deserve the highest focus on continuous improvement and planning since the associated efficiency gains are often immediately quantifiable. This paper will focus on the improvement and optimization of post frac cleanout and milling strategies in extremely depleted wells in the Sultanate Of Oman. The gains from such optimization helped improve wells delivery and overall performances. Plug and perf methodology is still the preferred placement method of hydraulic fractures. One of the main challenges in depleted wells is the need for cleanout and plug milling after each stage to avoid risk of CT becoming stuck either differentially due to depletion or mechanically with plug cuttings in case circulation is lost. For years the frac and mill concept was adopted to complete those wells, resulting in frequent delays to frac operations and huge cost impact to the overall project. An efficiency improvement plan was agreed upon to address this particular challenge. A step-by-step strategy improvement plan was developed via in-depth analysis of frac initiation and reservoir characteristics in order to combine together multiple stages of post-frac cleanout and milling activities. This was done through unique software simulations and fluid selection criteria to achieve the lowest possible bottom hole pressure to minimize the losses in addition to the highest possible lifting velocity and best carrying medium conditions. Moreover, the utilization of engineered fluid solutions with foaming agent and foam generator have demonstrated significant added value through enhancement of carrying fluid properties while achieving the lowest possible settling velocity, which in turn lead to the highest possible velocity factor. After completing the agreed optimization plan, a post frac cleanout with 6-plug milling was performed in a single combined stage instead of multiple individual stages. This improvement reduced the overall frac operation for 6 stages from nearly 30-35 days to 19-20 days. Understanding the field and reservoir pressures in addition to fluid selection for both post frac cleanout and milling operation is crucial to successful implementation of this methodology. This achievement was delivered through a collaboration between many different business units from design to execution and it will help Petroleum Development Oman PDO on the future planning of hydraulic fracturing activity. The completion of the entire wells (well delivery) was achieved in a significantly shorter period of time compared to previous wells; this is reflected on actual cost reduction of more than 20% of total cost/AFE.

In south-eastern part of the Sultanate of Oman, PDO is producing from one of Tight Sour Field (with H2S 1-2%) with current reservoir pressures ranging from 40,000 to 60,000kpa for more than 20 yrs. Due to tight nature of reservoir, the wells are hydraulically fracced to produce, but with time the production rates decline and wells start to produce in unstable mode. This unstable production mode leads to huge scaling and corrosion issues which results in tubing failures requiring huge and expensive workover to restore well production. Due to low production rates and expensive workover makes these intervention very less attractive in terms of Net Present Value (NPV) compared to other opportunities. This paper describes the challenges in restoring production from wells with tubing leaks using conventional workover techniques and the advantages of using new approach of using Hydraulic Work Over Unit (HWOU/Snubbing unit) to workover these wells. Using HWOU for workover restoration time from the failure to restoring production has been reduced from ~2-3yrs to almost less than a year along with significant reduction in overall cost (more than 40% per well). This approach has been successfully applied to 2 wells till dates and upcoming workover will be done in similar manner.