The injection of drilling generated waste into a selected subsurface formation has evolved into the most preferred waste disposal technology in terms of environmental compatibility and cost effectiveness, especially for remote and environmentally sensitive areas. The main principle of waste injection (WI) is the initiation of hydraulic fracture and the placement of solids within the created fractures through the high-pressure pumping of slurry batches. The fracture propagation is governed mainly by in-situ stresses. As injection progresses solids accumulation in the fracture leads to an increase of in-situ stresses within the injection zone causing a build-up of injection pressure. As allowable injection pressure is often limited by equipment, the undesirable or rapid injection pressure build-up could jeopardize the operational life of an injection well and limit its waste disposal capacity. This paper introduces a new approach to a regular seawater injection by investigating the relationship between pressure behavior and seawater injection. Displacement of slurry from the tubing by seawater over flush is carried out routinely in WI operations worldwide. However, never before it was considered as a pressure maintenance tool. The authors describe the impact of continuous seawater injection on injection pressure through the lifetime of three waste injectors. The injection pressure behavior before, during and after continuous seawater injection was reviewed using downhole measured data. It was noticed that regular seawater over-displacements during the continuous time periods between slurry injections reduced injection pressure considerably. Consequently, a thorough evaluation was initiated to investigate the impact of extended seawater injection on in-situ stresses and its potential advantage in maintaining the injection pressure within lower limits. Considering the novelty and value of study for expanding worldwide WI operations, this paper presents the new approach to seawater injection as an injection pressure and disposal capacity maintenance tool. Introduction In the early 1990s, WI emerged as a new technology that could provide an environmentally safe and economically sound solution to the disposal of drill cuttings and associated wastes in environmentally sensitive and remote operations. It was identified as one of the few technologies able to provide a complete drilling waste disposal solution that eliminates the need to accumulate, store and haul cuttings to shore for treatment. First pioneered with small volume annulus injections in the Gulf of Mexico in the mid-1980's the technology has since gained broad use in the North Sea, Alaska and other areas where the environmental conditions, tight regulations and logistics made this a viable drilling waste management option.1, 2 WI has been implemented successfully in the Caspian Sea since 2006, despite a complex subsurface environment and tectonics that presented significant technical challenges for vigilant monitoring and pressure interpretation as injection progresses.3 Pressure follow-up was recognized as critical to ensuring the safe and long-term containment of the waste to be injected.

The subsurface injection of drilling waste has become an increasingly popular and well-accepted technology over the last several decades. The popularity of this technology is primary spurred by its economic advantages in meeting more stringent drilling waste management requirements, especially in remote and environmentally sensitive areas. Furthermore, its use has become more attractive with the dramatic development and improvement in the processes associated with surface and sub-surface engineering, fracture modeling, risks identification and mitigation options, injection monitoring and in-depth pressure analysis. Together, these advancements have improved considerably the assurance and efficiency of waste injection operations worldwide. Nevertheless, despite the tremendous advancements in the fracture modeling attained from subsurface feasibility studies, a major uncertainty exists with the propagation of multiple-fractures that apparently accompanies the intermittent batch injection process, essential to the drilling waste injection operation. The propagation of multiple-fractures, along with their orientation and complexities, strongly influence the fracture design, ultimate disposal capacity and injection pressure behavior. Consequently, this uncertainty is a critical issue, both in drilling waste injection and re-fracturing in conventional stimulation treatments. This paper describes the evolution of understanding of multiple-fracture mechanics in drilling waste injection, starting from the conventional "wagon-wheel" uniform disposal-domain concept to the branching multiple-fractures approach that becomes practical through mathematical computations of near-wellbore changes in the stresses resulting from prior fracture creation and solids accumulation. Moreover, the authors present four potential scenarios of subsequent fracture initiation and propagation during intermittent injections, and provide revised re-assessment of data from the joint industry Mounds Drill Cuttings Injection Field Experiment.

fax 01-972-952-9435. AbstractThe progression of new field developments, including brownfield and deepwater, subsequently increases the volume of cuttings and production waste, and particularly produced water, considerably. The economical impact of missing drilling and production targets due to the failures in the drilling waste injection process represents high risks that demand sound engineering processes to ensure injection assurance.This paper describes the solution and detailed pressure monitoring methodology implemented to maintain safe injection assurance via regular disposal fracture diagnostics. Timely identification and a thorough evaluation of non-ideal pressure signatures observed during injection and post shut-in periods provided critical information required to detect subsurface anomalies. This can be an effective tool for the subsurface risks identification and characterization.The application of comprehensive fracture-mapping techniques is a major step in mitigating the environmental risks posed by waste. Waste mapping represents valuable information, not only in the overall planning of drilling operations, but in the fundamental and invaluable need to provide sound engineering for waste location and fracture containment assurance, thus minimizing environmental impact. Previous, oversimplified interpretations of multiple fracturing systems (or so-called uniform disposal domain) and new fracture initiation process are demonstrated to be in apparent conflict with fracture mechanics, stress calculations and the general principles of physics.The authors also describe the results of pressure analysis conducted in a North Sea injection well, which simultaneously was used for production. The well was utilized successfully for Cuttings Re-Injection (CRI) and for the disposal of produced water. The success of the operation was a direct result of close monitoring of key injection parameters and indepth analysis of injection pressure, despite risky geological conditions. Abnormal pressures increases and restrictions observed during injection were mitigated and addressed via a proper root-cause engineering and sound pressure diagnostic process. The drilling waste injection took place below a 13 3/8-in. casing shoe through the B annulus, in an open-hole section at the depth of 1220m TVD with a 24 0 deviation in the injection interval. The injection took place in close proximity to a major fault axis.

The South part of the Priobskoe field, located in Western Siberia on a flood land of the Irtysh River, is an environmentally sensitive area. Zero discharge regulations prohibit cuttings discharge and spills of liquid wastes on the surface. Until now, the exploration and full development of such oil and gas fields was a major challenge for operating companies working in Russia as all drilling wastes including cuttings, used muds ready for disposal, and waste waters which cannot be disposed in this sensitive area. Drilling wastes had to be transported away from the region to areas where waste disposal pits were allowed to be constructed and wastes to be stored. The major hurdle for the drilling campaign is the cost of transportation of the vast amount of drilling waste generated from multiple rigs. Moreover, during spring or fall, such transportation is virtually impossible because of the absence of winter roads and rivers are impassable due to flooding or ice movement. A joint effort between a major oil company in Russian and a waste management service company selected Waste Injection (WI) technology as the most efficient, economical and environmentally friendly way to handle the drilling waste in the field. Waste Injection is a relatively new waste disposal methodology used in Russia, although the first injection job on a worldwide basis was in 1991. The first Russian WI operation was successfully implemented in 2004 on offshore projects near Sakhalin Island. Since that time and until October 2008, WI had only been used on several offshore platforms. The need of a robust technology for waste management on the South Priobskoe field was the departure point for implementing WI in mainland Russia. The following paper describes the steps taken to implement WI on land projects in Russia as the technology that allows for zero discharge, ensuring a safe and permanent drilling waste disposal performed under strict regulations and minimizing associated transportation and cost risks. Waste Injection Assurance Most of the oil companies in Russia wanted to implement WI on the mainland but were concerned about legislation issues as this type of operation had never been done on Russian land jobs. In October 2008, the first steps towards making WI operations a reality in Russia began with the development of a feasibility study or Front-End Engineering Design (FEED) Study for waste injection in the area, as part of the assurance process.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe volume of cuttings and produced waste, particularly produced water, will increase as brownfield developments progresses. Missing environmental and economic targets represent a major investment exposure. As a resut, there is an increasing demand on engineering to mitigate process risks and ensure injection and sound subsurface waste management.This paper describes the outcome of pressure analysis successfully used for Cuttings Re-Injection (CRI) and disposal of produced water resulting from closely monitoring pressure injection and decline. It addresses proper root-cause engineering diagnostic processes that were implemented during abnormal pressures increases and restrictions observed during annulus injection in North Sea projects.Severe risks were mitigated with injection pressures observed, on occasion above overburden, to maintain safe injection assurance. A methodology was developed and implemented, as a result of process mapping based on signature pressures from pressure decline. Their characterization represents a major step in mitigating risks posed by waste injection, providing not only engineering understanding valuable to overall drilling operations planning, but also minimizing potential environmental impact with sound engineering subsurface waste management.