Managed Pressure Drilling and Underbalanced Drilling Compounded Role in Solving the Exploration and Appraisal Challenges of Biogenetic Gas Resources in the United Arab Emirates -Case Study

Biogenic gas resources have gathered importance recently due to its widespread availability, occurrence at geologically predictable circumstances, and existence at shallow depths. It is estimated that biogenic gas forms more than 20% of the global discovered reserves. However, the exploration and development of these unconventional resources come with numerous drilling and reservoir challenges. This paper showcases a novel approach used in the United Arab Emirates to overcome these challenges using managed pressure and underbalanced drilling. To tackle both reservoir and drilling challenges, a hybrid solution combining Underbalanced (UBD) and Managed Pressure Drilling (MPD) was applied. UBD was used to characterize the reservoir in terms of pressure and productivity index to ultimately enhance productivity by eliminating formation damage. MPD was used next to continue drilling through the problematic zone which had high instability due to the presence of highly sensitive salt, in addition to the presence of high pressure and loss zones. The fit for purpose hybrid application design allowed the operator to immediately switch between UBD and MPD conditions, as the well required with the same equipment. Three of the four targeted formations were in the 8 ½″ hole section, UBD was selected to drill the first reservoir formation which allowed pore pressure verification and avoided using excessive mud weight that was the culprit of many challenges like slow ROP, drilling fluid losses, bit balling, and fracking the formations. UBD has proved that mud weight can be reduced by 20%-30% comparing to conventional drilling. The second formation was a salt formation that has caused previously hole collapse and losses-kicks problems as heavy mud used to drill this salty formation. MPD used successfully drill this section by constant bottom hole pressure and lower mud weight as it was found from analyzing offset wells reports that hole collapse occurred at connections and pump off events. Constant Bottom Hole Pressure (CBHP) also eliminated tight spots and excessive reaming resulting in optimized drilling. The third formation used MPD as well to minimize overbalance pressure over previous sections while the fourth formation was drilled by UBD as it had a separate 6″ hole section as it formed an independent reservoir. The combined MPD and UBD approach eliminated most the NPT encountered in offset wells, enhanced Rate of Penetration (ROP) by 200% to 300% and slashed the well drilling time by 27 days.

Study on the Rheological Properties of Ultra-High Temperature CGA Drilling Fluids

Colloidal gas aphron (CGA) drilling fluids are a kind of environmentally-friendly underbalanced drilling technique, which has attracted more attention in depleted reservoirs and other low-pressure areas. With the shortage of global oil/gas resources, drilling has gradually shifted to high-temperature and deep wells. Hence, a study on the ultra-high temperature rheology properties of CGA fluids is lacking and urgently needed. In this study, a novel CGA drilling fluid system was prepared by modified starch and amino acid surfactant, and rheological properties after 120-300°C aged was investigate. Results show that: (1) Herschel-Bulkley model is the preferred model to predict CGA drilling fluid at ultra-high temperatures; (2) It was proved that CGA drilling fluid is a high-quality drilling fluid with extremely high value of LSRV and shear thinning property within 280°C. Compared to the traditional XG-based CGA drilling fluid, the improvement of LSRV at ultra-high temperatures is a significant advantage of EST-based CGA drilling fluid which is conducive to carrying cuttings and sealing formation pores.

A Smart Classification Framework for Enhancing Reliability in Downhole Gas Bubble Sensing

Production logging tools (PLTs) and formation testing, even in logging while drilling (LWD) conditions during underbalanced drilling, are key technologies for assessing the productivity potential of a gas well and therefore to maximize recovery. Gas bubble detection sensors are key components in determining the fluid phases in the reservoir and accurately quantify recoverable reserves, optimize well placement, geosteering and to qualify the production ability of the well. We present here a new nonlinear autoregressive - breakdown artificial intelligence (AI) detection framework for PLT gas bubble detection sensors that categorize in real-time whether and which sensors become unreliable or have broken down during the logging measurements. AI tools allow the automatization of this method that is critical during data quality control of post-drilling PLT, but it is essential when the measurements are performed in LWD as data assessment and processing need to occur in real time. This AI framework was validated on both a training and testing dataset, and exhibited strong classification performance. This method enables accurate real-time breakdown detection for gas bubble detection sensors.

Application of Laser and Plasma for Thermal Assisted Drilling in Carbonated Formations

Employing novel drilling, and tunneling methods are active area of study since 1930s. In the present report, an Experimental study of the thermal impact of laser and plasma torch on carbonated rocks as part of thermal assisted drilling operation is presented. The experimental findings are then evaluated and verified by the Kirch's equations for stresses and strains around a cylindrical borehole. Since it is vital to carefully studying the wellbore stability in this type of drilling method, especially if it is associated with underbalanced drilling (UBD) and or Managed pressure drilling (MPD), further numerical investigations are carried out to highlight the necessary considerations in this regard.

Modeling the Pressure Transverse for Foam Drilling Operation in Vertical Well

Pressure transverse in foam drilling operation is sensitive and difficult to predict particular at the start of flow that follows the unavoidable shut in due to inevitable procedure of stop and proceed arising from re-connection of additional drilling pipe to further drill depth. The practice in drilling may not enable the flow to attain steadiness flow region before running in the length of drill pipe. Most existing models in the literature for predicting pressure transverse in foam drilling operation only captured the steadiness flow region of the foam drilling operation by keeping out restriction terms induced by accumulation and kinetic for simplicity sake, hence unsteadiness flow region experienced during foam drilling operation was rarely modelled. It is highly expedient to derive a model that evident the unsteadiness region in order to accurately predict pressure transverse, hence sufficiently analyses the well stability during foam drilling operation. In this study, a model for forecasting pressure transverse in foam drilling operation was established considering restriction term caused by accumulation and kinetic that constitute for accurate formulation of hydraulic model that govern flow of foam during underbalanced drilling. By applying the proposed model to a case study reported in literature, pressure transverse at unsteadiness flow region for foam drilling operation can be quantitatively estimated and analyzed. The result obtained in a case study carried out indicates high variance in pressure as function time at the beginning of flow in foam drilling where unsteadiness is promoted before matching up closely with the results obtained from the existing Guo et al 2003 model at the steadiness flow region. The new model has a better accuracy with a percentage error of 0.74% and 6.4% as compared to previous models by Guo et al 2003. The proposed model make possible for drilling engineer to take decision with larger precision during hydraulic design of foam drilling operation and guaranteeing well stability in complex drilling system.

Unlocking Oman's Tight Gas Potential using State-of-the-Art Underbalanced Coiled Tubing Drilling Technologies

With the large amount of tight gas reserves remaining in Oman, new innovative techniques and methods to unlock these reserves have become imperative for the future economic success and stability of the country. Among the various technologies considered, the concept of underbalanced coiled tubing drilling (UBCTD) was introduced. In order to address the harsh downhole challenges such as high temperatures, deep burial depths, under pressured reservoirs, abrasive and hard sands and logistical constraints; a fully integrated well delivery solution was developed jointly by the operator and energy service company. In accordance with this strategy, best in class downhole drilling tools, a state-of-the-art fully automated coiled tubing drilling unit together with technical and project management experts were deployed. Application specific solutions to the challenging subsurface conditions included utilization of underbalanced drilling (UBD) techniques, deployment of high temperature drilling assemblies, fit-for-purpose bit drive mechanism and a robust integrated management system. All of the above was achieved whilst ensuring the safety of all personnel during the project and reducing carbon emissions through a flare minimization strategy and diesel consumption reduction initiatives. Over the course of the pilot campaign, reservoir exposure per well was doubled, average penetration rate compared to conventional rotary drilling was more than tripled and incremental production improvements of up to 230% were observed. This paper discusses the challenges faced and the solutions implemented during this three well pilot campaign.

A Novel Approach for Underbalanced Well Completions in Depleted and Highly Fractured Carbonate Reservoirs

A prime objective of oil and gas operators is to maximize reservoir productivity and increase the ultimate recovery from all depleting fields. Underbalanced drilling is one such enabling technology that has been adopted world wide to achieve a number of objectives in maximizing the reservoir potential. Chief among these objectives are to reduce formation invasion damage, identify sweet spots in the reservoir, and reduce well costs. Underblanaced operations however introduces more complexity into the successful drilling and completion of a candidate well. An improperly executed underbalanced operation can result in having less productivity in contrast to a conventionally drilled and completed well. Pakistan a country currently highly dependent on foreign hydrocarbon fuels, once had total independence in at least natural gas. The southern part of Pakistan is known for its rich hydrocarbon potential, but most fields were discovered decades ago and have depleted at a rapid pace. Numerous fields in the vicinity have depleted to an extent that the reservoir pressure has reduced to a mere 3.9 PPG in EMW. In the most recently drilled well the pressure depletion caused massive circulation losses while drilling the reservoir formation and the operator had resorted to pumping of heavy LCM pills and blind drilling to complete the section. After completing the well conventionally the operator made multiple attempts to kick off the well but observed no production. Subsequently multiple acid stimulation jobs were performed to reduce the formation damage, but all efforts were in vain. It was evaluated that the heavy LCM and drilled cuttings had bridged off and choked the reservoir skin completely from which there was no return. Ultimately the well had to be plugged and abandoned. In relatively higher pressured and non-fractured formations the option exists to drill a well in underbalanced mode and trip the running string by balancing the well with a light weight fluid. For the subject case however, this option was impossible due to the highly fractured nature of the formation. A plan was devised to include a downhole casing isolation valve in the last casing string and drill the well with an extremely light weight multiphase fluid. A rotating control device would be used to strip the running string in and out of the well. The completion packer was also to be stripped into a live well and set in place without the need of ever killing or balancing the well. By executing the mentioned methodology, the operator was able to drill and complete a well all the while keeping the reservoir formation in a virgin state. The paper discusses the planning, design, execution, and lessons learnt in underbalanced drilling and completion operations in the subject field.

Case Study of Underbalance Coiled Tubing Drilling to Increase Well Productivity and Ultimate Recovery in Tight Gas Reservoir Onshore Field, Abu Dhabi

Coiled Tubing Drilling (CTD) has been growing and developed rapidly through the last two decades. There have been numerous highly successful applications of CTD technology in Alaska, Canada, Oman and the United Arab Emirates (Sharjah Sajaa and Dubai Murgham fields), among other places. Currently, Saudi Arabia has undertaken a campaign for the last seven years that has shown successful results in gas reservoirs. ADNOC initiated a trial Coiled Tubing Underbalanced Drilling (CTUBD) project in the onshore tight gas reservoirs in Abu Dhabi, United Arab Emirates beginning operations 1-December-2019. The initial trial will consist of three (3) wells. The purpose of the trial is to assess the suitability of CTUBD for drilling the reservoir sections of wells in these fields, and further application in others. The reason for choosing coiled tubing for drilling the reservoir sections is based upon the high H2S content of the reservoir fluids and the premise that HSE can be enhanced by using a closed drilling system rather than an open conventional system. The three wells will be newly drilled, cased and cemented down to top reservoir by a conventional rig. The rig will run the completion and Christmas tree before moving off and allowing the coiled tubing rig to move onto the well. The coiled tubing BOPs will be rigged up on top of the Christmas tree and a drilling BHA will be deployed through the completion to drill the reservoir lateral. The wells will be drilled underbalanced to aid reservoir performance and to allow hole cleaning with returns being taken up the coiled tubing / tubing annulus. The returns will be routed to a closed separation system with produced gas and condensate being primarily exported to the field plant via the production line, solids sparge to a closed tank or pit and the drilling fluid re-circulated. The primary drilling fluid will be treated water; however, nitrogen may be required for drilling future wells in the field and will be required regardless for purging gas from the surface equipment during operations. A flare will also be required for emergency use and for start-up of drilling. If the trial proves a success, a continuous drilling plan will be put in place.

A novel artificial intelligence automatic detection framework to increase reliability of PLT gas bubble sensing

Production logging tools (PLTs) and formation testing, even in logging while drilling (LWD) conditions during underbalanced drilling, are key technologies for assessing the productivity potential of a gas well and therefore to maximize recovery. Gas bubble detection sensors are key components in determining the fluid phases in the reservoir and accurately quantify recoverable reserves, optimize well placement, geosteering and to qualify the production ability of the well. We present here a new nonlinear autoregressive - breakdown artificial intelligence (AI) detection framework for PLT gas bubble detection sensors that categorize in real-time whether and which sensors become unreliable or have broken down during the logging measurements. AI tools allow the automatization of this method that is critical during data quality control of post-drilling PLT, but it is essential when the measurements are performed in LWD as data assessment and processing need to occur in real-time. This AI framework was validated on both a training and testing dataset, and exhibited strong classification performance. This method enables accurate real-time breakdown detection for gas bubble detection sensors.