Lost circulation is a common problem in the massive Simsima and Umm El Radhuma carbonate formations that extend across all United Arab Emirates fields and the Gulf countries. To minimize losses during drilling, 8.10-lbm/gal emulsion mud or aerated mud is often used. As the result of corrosive brines presence across the formations extending to the shallow depths and causing casing corrosion problems, one of the main objectives of cementing the 9 5/8-in. casing is to ensure well integrity and casing protection by having cement to surface. In these carbonates, multistage cementing tools have operational problems and frequently develop casing leaks over the life of a well. Top jobs do not guarantee complete linear and radial coverage of the casing along the whole interval. Complete losses are expected with conventional lightweight cement systems, and their set cement properties do not meet requirements for casing corrosion protection. These issues make successful cementing in these formations a real challenge. To overcome the challenges, a new ultralightweight cement system (ULC) with a density close to that of water and superior set cement properties was used to ensure good casing protection and zonal isolation. This paper addresses the challenge to measure the low density of the slurry and the tools necessary to differentiate between mix fluid and the final slurry. The new ultra-lightweight cement was evaluated using standard cement evaluation logs, and case studies are presented that confirm successful zonal isolation. Background Protecting the casing against corrosive brine attack is the best way to extend the life of a well. Abu Dhabi Company for Onshore Oil Operations (ADCO) desired a 50-yr well life. To achieve this goal, it was essential to obtain the best primary cement job possible. Using high-performance lightweight (HPLW) cement and eliminating the stage collar for multistage cementing were two of the means applied successfully.1 In some of the applications, the very weak formations experienced losses during the primary cement jobs despite the use of HPLW cement systems with densities as low as 10.5 lbm/gal. Lost circulation problems continued until development of a new ULC system, with a density range that encompasses the density of water, that provided the set cement properties necessary to protect against corrosive brine attack and extend the life of the casing. ADCO Different Casing Schemes: Different casing schemes in ADCO's operations can generally be classified into three main groups (Fig. 1). Group 1: Light Casing Design for Development Wells The 13 3/8-in. surface casing is set at the uppermost hard formation (Rus) to cover two problematic formations: the unconsolidated Miocene formation and the shallow water-bearing Dammam formation, where lost circulation problems are common. The 9 5/8-in. production casing is set at the top of the reservoir to cover three problematic formations: the Umm Er-Radhuma (UER) and Simsima, which are water bearing and experience lost circulation, and the water-sensitive Nahr Umar shale formation. The cement job of the 9 5/8-in casing is critical as this casing is the only barrier against the corrosive aquifers of UER and Simsima.

Lost circulation is a common problem in the massive Simsima and Umm El Radhuma carbonate formations that extend across all United Arab Emirates fields and the Gulf countries. To minimize losses during drilling, 8.10-lbm/gal emulsion mud or aerated mud is often used. As the result of corrosive brines presence across the formations extending to the shallow depths and causing casing corrosion problems, one of the main objectives of cementing the 9 5/8-in. casing is to ensure well integrity and casing protection by having cement to surface. In these carbonates, multistage cementing tools have operational problems and frequently develop casing leaks over the life of a well. Top jobs do not guarantee complete linear and radial coverage of the casing along the whole interval. Complete losses are expected with conventional lightweight cement systems, and their set cement properties do not meet requirements for casing corrosion protection. These issues make successful cementing in these formations a real challenge. To overcome the challenges, a new ultralightweight cement system (ULC) with a density close to that of water and superior set cement properties was used to ensure good casing protection and zonal isolation. This paper addresses the challenge to measure the low density of the slurry and the tools necessary to differentiate between mix fluid and the final slurry. The new ultra-lightweight cement was evaluated using standard cement evaluation logs, and case studies are presented that confirm successful zonal isolation. Background Protecting the casing against corrosive brine attack is the best way to extend the life of a well. Abu Dhabi Company for Onshore Oil Operations (ADCO) desired a 50-yr well life. To achieve this goal, it was essential to obtain the best primary cement job possible. Using high-performance lightweight (HPLW) cement and eliminating the stage collar for multistage cementing were two of the means applied successfully.1 In some of the applications, the very weak formations experienced losses during the primary cement jobs despite the use of HPLW cement systems with densities as low as 10.5 lbm/gal. Lost circulation problems continued until development of a new ULC system, with a density range that encompasses the density of water, that provided the set cement properties necessary to protect against corrosive brine attack and extend the life of the casing. DCO Different Casing Schemes: Different casing schemes in ADCO's operations can generally be classified into three main groups (Fig. 1). Group 1: Light Casing Design for Development Wells The 13 3/8-in. surface casing is set at the uppermost hard formation (Rus) to cover two problematic formations: the unconsolidated Miocene formation and the shallow water-bearing Dammam formation, where lost circulation problems are common. The 9 5/8-in. production casing is set at the top of the reservoir to cover three problematic formations: the Umm Er-Radhuma (UER) and Simsima, which are water bearing and experience lost circulation, and the water-sensitive Nahr Umar shale formation. The cement job of the 9 5/8-in casing is critical as this casing is the only barrier against the corrosive aquifers of UER and Simsima.

The process of sidetracking an existing borehole with a balanced cement plug has historically been time consuming and problematic for the drilling industry.In many instances long drilling times or even multiple plugs are required to achieve the objective of sidetracking the well. These problems lead to increased drilling time and increased cost for the operator. Traditional cement slurry systems for sidetrack applications have been focused on the development of high compressive strength through reduced water content. Conventional high compressive strength cement systems exhibit low resistance to impact and low resistance to fracture propagation through the set cement. Recent developments in oil well cement system have incorporated a unique micro-ribbon technology with an optimized particle size distribution to increase the durability, load bearing capacity and resistance to fracture propagation of set cement. Field tests with these cement systems have shown substantial improvements over conventional cement slurries in terms of plug success rate and time required to achieve the objective of sidetracking the well. These improvements have resulted in significant reductions in the total cost of the operation of sidetracking wells. This paper will discuss the improved mechanical properties of these new cement systems and the success of the numerous field tests. Introduction Borehole sidetracking operations with cement plugs is a well-established and long-standing technique. This technique consists of placing a plug of cement in the borehole, allowing the cement to establish compressive strength, then using the cement plug to deflect the bit away from the current borehole starting anew open hole section. Difficulties in this operation are also well documented and long-standing [1–6]. As drilling cost increased and the level of directional drilling increased the cost associated with the failures of sidetrack cement plugs gained more attention. These problems continue to receive attention today. Many studies have been conducted to improve success rates of open hole kickoff plug placement [1–4]. Most of these studies have focused on improving portions of the workflow process associated with plug placement and slurry design methods. Others have focused on developing recommended practices for the sidetracking operation as a whole [2]. New tools have been proposed and developed to improve the placement efficiency of cement slurries [5–6] or provide mechanical alternatives to cement plugs in the open hole [6]. Much less effort has been directed toward optimizing the cement systems utilized to achieve the sidetrack. Traditionally, cement system design for sidetracking operations has focused on maximizing set cement compressive strength while optimizing other traditional properties such as pumping -time, rheology, slurry stability, fluid loss, etc. Some work has been focused on the development of cement systems that reduce the rate of penetration when drilled[7]. This work has been focused on the addition of particles with a high degree of hardness to the slurry. Reducing the rate of penetration of the slurry when drilled would seem to represent an important characteristic of aset cement system used for sidetracking operations. When properly applied, these lessons learned and the cumulative set of placement and design methodologies developed from past efforts have provided substantial rewards to the industry. However in some areas, for example regions with extremely hard formations, problems still exist even if proper placement and proper conventional slurry design are followed. This paper will outline a new cement slurry that focuses on optimizing the mechanical durability of the set cement through the implementation of optimized particle size distribution slurries with metallic micro-ribbon technology and the successful field testing of these slurries in over 25 wells. Successful implementation of this new system in sidetracking operations for a major operator in Abu Dhabi has resulted in significant improvements in the efficiency of sidetracking operations and significant cost reductions resulting from rig time saved.

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ADCO has always been seeking continual improvement to minimise the impact of its drilling operations on the environment and to conserve the desert for future generations. One of the main challenges is proper management of the fluids & solids generated by drilling oil & gas wells. This paper presents the complete solutions adopted to handle the generated waste streams with the improvements in rigs design ("zero" discharge) and the execution of three recent plants:Reconditioning & recycling plant for drilling Oil-Based Mud (OBM).Indirect thermal desorption treatment plant for OBM drill cuttings with 100% recycling of recovered materials which are converted to usable products (i.e., diesel fuel, irrigation water and interlocking blocks).Two dedicated deep disposal wells for waste mud. The outcome of the joint efforts of Drilling & HSE Divisions confirms that all hazardous wastes are being managed with true applications of 3R (Reduce, Reuse and Recycle) to maximise hydrocarbon recovery without noticeable impact on the environment. The new waste management plants are centrally located in the major oil producing fields, thereby reducing hauling distance. These improvements translate in ADCO to minimum disposal and overall costs saving while ensuring compliance with or even exceeding, local environmental regulations. Such global approach of this scale is a first in the Middle East Region and is setting a new benchmark of environmental standards for others to follow. Introduction Drilling oil wells produce large quantities of solid waste drill cuttings and also fluids that must be properly managed to prevent negative impact on human health and the environment. The fluids comprised of drilling mud or brines used in each section of the well. The potential health and environmental hazards are fluids containing large amount of oil (diesel-based mud or OBM) or salts (high salinity water-based mud & completion brines). The solids are the cuttings removed from the hole. They do not present any hazards by their natural minerals but, if generated during drilling with OBM, they are contaminated by 20 to 30 % of oil, which require further treatment before final disposal. Currently, ADCO is producing an estimated 20,000 tons of oily cuttings and about 900,000 barrels of waste fluids have to be disposed off every year. Environmental legislation prohibits disposal of oily wastes into the environment. Waste Management Strategies For many years, ADCO Drilling Division has been increasingly confronted with problems relative to transporting oily cuttings over 300 km from the rig to a designated site for storage and disposal. Expensive OBM (diesel base) was reused few times at other rigs before injection into well annulus. The concept of zero waste discharges from drilling operations was being taken to new levels to develop zero contaminants discharge policy through implementing waste management principle of the three golden rules: REDUCE, REUSE & RECYCLE. The first move is to minimise as much as practical the amount of waste generated ("REDUCE"). Over the years, the following had been implemented in this regard:1. Reduce the hole diameter (less cuttings generated & less mud to be disposed off) by optimising the well casings program for every single well ("light casing program" whenever feasible).2. Eliminate the use of "emulsion" mud (oil added to WBM to reduce weight) in loss circulation zones by using "Aerated mud" (compressed air added to reduce weight).3. Improve the efficiency of the solid control equipment installed on the rigs ("state of the art" shale shakers and rented "Hi-G" dryers & centrifuges) to reduce the need for dilutions & limit the amount of oil on cuttings.4. Strive to reduce OBM usage by assessing & trying new inhibitive water mud systems (Silicate mud for example).