Managing environmental impacts associated with drilling is a challenge to oil & gas ompanies and in recent year more efforts are exerted in increasing production levels hence increasing drilling activities and associated environmental concerns. Key environmental issues associated with onshore drilling activities include release to the atmosphere & groundwater and generation of hazardous wastes. Over the last few years, ADCO has intensified its drilling activities to meet challenging production targets and over the last 10 years number of drilled wells has almost doubled. In order to minimize environmental impacts of drilling activities addressing environmental issues became central to work planning and regarded as a business objective. The majority of drilling wastes includes drilling fluids & cuttings and if these are not managed effectively they may result into soil & groundwater contamination and could harm to biota. In order to minimize the environmental impact of drilling waste an integratedwaste management scheme was developed to implement Zero Discharge and 100% HSE concepts from drilling locations and this scheme includes: Two waste disposal wells for Water Based Mud (WBM) for injection in the deeper aquifers. Reconditioning of Oil Based Mud (OBM) at reconditioning plant for reuse Thermal Desorption Unit (TDU) for treating OBM Cuttings In 2017, approximately a Million feet of wells were drilled resulting in generation of 200,000 tons of WBM cuttings and 40000 tons of OBM cuttings. OBM Cuttings were treated at TDU and 12000 bbls of oil was recovered. In addition, approximately 100 K bbl. of waste WBM and other drilling fluids were injected in deeper formation. 99.9% of oil from OBM cuttings is reclaimed as a fuel and the final inert material used for manufacturing cement blocks. The outcome the solution is converting drilling hazardous wastes through 100 % recycling into environmentallyfriendly and beneficially-used products. The concept of 3Rs- Reduce, reuse& recycle is applied for managing drilling waste to protect the environment.

The conventional drilling fluid to drill the high-temperature wells are non-aqueous fluid. ADNOC used high-temperature water-based drilling fluid instead of nonaqueous fluid to drill the well successfully. High-temperature water-based drilling-fluid systems hold several advantages over non-aqueous systems from financial and environmental viewpoints. However, most conventional water-based systems start to become unstable at temperatures above 300 degF. This paper details the design and implementation of specially designed water-based drilling fluids based on custom-made branched synthetic polymer that meet these temperature stability requirements. The branched synthetic polymer exhibits superior rheological properties and fluid loss control, as well as longterm stability above 400 degF. Under static conditions, the high-temperature fluid shows no gelation, resulting in lower swab surge pressures while the stability of the highly branched synthetic polymer and enhanced rheological profile minimize sag. ADNOC required a cost-effective drilling-fluid system that remains stable under static temperatures expected to exceed 375 degF. The longterm stability of the system was critical for successful wireline logging operations. In addition, the system was required to provide shale inhibition, hydrogen sulfide (H2S) suppression and enough density to maintain well integrity while drilling through anticipated high-pressure zones. The challenging intermediate and reservoir sections were drilled and evaluated using high temperature water-based system. This paper will discuss the successful execution of high temperature water-based system in one of high-temperature well in ADNOC field.

The objective of this paper is to demonstrate the challenges, solutions and results of performing offshore Drilling Waste Management operations in a highly environmentally sensitive marine environment and UNESCO World Biosphere Reserve in offshore Abu Dhabi. The solution was to treat all drilling waste at source. This required both NOV Thermal Treatment Technology and NOV Cuttings Re-Injection Technology and became the World's first single-source operation for this equipment. The equipment was shipped to the island, installed and operated in parallel with the Operator's drilling programme. The drilling waste (Oil-Based Mud) was handled and stored by EMDAD then processed through the NOV Thermal treatment unit, which generated three separate treated waste streams - oil, water and solids. The recovered oil and water were reused on-site, whilst the treated solids were slurrified and fed to the NOV Cuttings Re-Injection system (CRI), which injected the solids into a disposal well. This paper will also demonstrate the results of the integrated operation.

Completion fluids, typically chloride or bromide brines, based on density requirements are used to control the well during some operations and remain either in the tubing until well is put on production or in the annulus above the packer for the duration of well life. Under normal conditions, the well casing is a closed system where the brine is protected from ingress of H2S/CO2 and oxygen. However, brines may be exposed to oxygen ingress from the surface through a leak at the wellhead, and /or to H2S / CO2 ingress through a potential leak through the packer, their dissolution in the brine, affecting significantly the corrosion resistance of the steel. In spite of its proven efficiency with martensitic stainless steels, sodium bromide based completion brines are quite expensive. To explore possible less expensive alternatives, without compromising corrosion resistance of the tubing, ADNOC Onshore conducted a comprehensive testing program to identify suitable, less expensive alternative brine systems with the same or improved corrosion behavior in well conditions. In the study, the general and pitting corrosion, and the Sulphide Stress Cracking (SSC) resistance of 13Cr and S13Cr samples in NaCl, NaBr and CaCl2 brines were assessed. Samples were tested for a period of 30 days in three brine systems, under inert conditions, under 1.6psi (6.5psi) H2S / 165psi CO2, at 120°C and under oxygen ingress conditions at 49°C, in an autoclave. Pitting and general corrosion were assessed using weight loss coupons, whereas the susceptibility to SSC was tested using C-ring specimens in accordance with NACE TM0177 - Method C, at stress levels of 0,2% of the material proof stresses. Relative pitting susceptibility of the steels under oxygen contamination of the different brine systems was also assessed by electrochemical polarisation tests, at 49°C. The most significant results obtained is that none of the steels presented SSC under all conditions and brine systems. For both alloys, in all test conditions, the general corrosion rates decreased in the order CaCl2 > NaBr > NaCl brines, the exposure to H2S/CO2 presenting 2 to 5 times higher corrosion rates as compared to the inert gas conditions, with the 13Cr alloy presenting higher rates in all conditions, as expected. Pitting was inexistent / negligible in all testing conditions for S13Cr. In sour environment and in oxygen ingress conditions, 13Cr showed relevant pitting in all brines. Under oxygen contamination, deeper and broader pits were observed in the NaCl as compared to the CaCl2 brine, while no pitting was found on NaBr brine specimens. Electrochemical polarisation tests showed that the pitting onset and the repassivation potentials were shifting towards the cathodic direction in the order NaCl, NaBr and CaCl2. The conclusions of the study is that chloride brine systems are a technically viable option for application with S13Cr, without introducing additional corrosion or HSE risks, leading to cost saving of $81MM over five years whereas for 13Cr, the use of bromide based brines cannot be avoided.

An active filter cake technology (AFT) was chosen to improve production performance in the tight reservoir following a comprehensive laboratory study to determine formation damage impact caused by previous non-damaging fluids (NDF). The AFT was successfully field trialed on two wells with production improvement vs. acid stimulated offset wells. This paper discusses laboratory data and improved field productivity. It documents reduction of torque/drag with increased rate of penetration without using a lubricant during drilling. Comprehensive laboratory testing to identify origins of deficient production was completed by thoroughly reviewing drilling and completion practices, and completion type implemented. Compatibility of base brine with formation water; formation damage impact of drilling fluids used in reservoir and effectiveness of hydrochloric acid (HCl) solution pumped through coiled tubing to destroy the filter cake constituted the first phase of the investigation. Assessment of several fluids capable of mitigating concerns was performed in the second phase. The optimization and customization of candidate fluids to address all challenges was the third phase. Last phase consisted of field trials and assessment of production results. Testing identified a potential incompatibility of calcium chloride brine and the formation water. The brine was replaced with monovalent halides brine. The previous NDF system exhibited elevated filtrate volume and a high concentration of acid insoluble materials which together significantly impacted productivity. Review of the completion operation and laboratory results proved filter cakes of reservoir drill-in fluids (RDF) cannot be homogenously and entirely removed with HCl solution using coiled tubing. Only less than 50% of the wellbore length can be accessed with coiled tubing and treated with acid. The acid treatment dissolved less than 10% of filter cake when sumulated field conditions in the laboratory. Likewise, the filter cake breaker cannot be implemented on barefoot completion as its volume is totally lost to the formation after breakthrough before complete filter cake dissolution occurs. The study recommended AFT with 100% organophilic bridging materials. The AFT was successfully field trialled in two wells. Post analysis of drilling parameters with AFT exhibits lower torques without addition of lubricant compared to previous fluid along with 186% increase in average rate of penetration which saved 79 hours of ILT/well. Production kicked-off without assistance from lighter fluid (N2 gas) or stimulation showing promising results compared with near-by wells. The 100% organophilic bridging materials were used for first time in field. It proved acid stimulation can be eliminated for the tight reservoir while improving the oil production rate compared to the offset wells. In addition to inherent productivity improvement characteristics, AFT is appropriate where cheesing and greasing of RDF are common problems with lubricants. AFT demonstrates reduced torque without lubricant addition in extended horizontal deviated wells and excellent production while eliminating post stimulation.