In Dallas Fort Worth (DFW), sewage is treated with a combination of anaerobic digestion, effluent filtration and lime stabilization to create biosolids which are then composted, landfilled, or land applied. The current treatment procedure has certain concerns including emissions or accumulation of odors, pathogens, nutrients, metals, and pharmaceutical products.<br/> An alternative method, the Slurry Injection technique, enables the digestion of biosolids in the deep earth and can replace the current practice of wastewater treatment or disposal in a much more environmentally friendly and cost-efficient manner. By completely sequestering methane and CO2 into deep geologic formations which are produced as biosolids breakdown, reduces the greenhouse gas emissions and enables the operator to create greenhouse gas emission offset credits which can be marketed to offset the operating costs.<br/> The economic, environmental, and technical aspects of building a new biosolids slurry injection facility in DFW, includes both the surface construction requirements as well as the subsurface strata evaluation for containment assurance. For the subsurface aspects, a geomechanical and stress analysis is performed on the Atoka formation (near the city of Fort Worth) and it confirms a confining layer above and below the injection zone to keep the waste contained for permanent storage.

Oilfields produce huge amount of waste on daily basis such as drilling mud, tank bottoms, completion fluids, well treatment chemicals, dirty water and produced saltwater. These waste types represent a real challenge to the surrounding environment especially when the oilfield is located within a sensitive environment as in the Western Desert where there are natural reserves and fresh water aquifers. Waste slurry injection has proven to be an economic, environmentally friendly technique to achieve zero waste discharge on the surface over the past years. This technique involves creating a hydraulic fracture in a deep, subsurface, non-hydrocarbon bearing formation which acts as a storage domain to the injected slurrified waste. The objective of this study is to evaluate the feasibility of waste slurry injection in an oil prospect located in the Western Desert. The evaluation includes assessing the subsurface geology, recognizing the possible candidate injection formation(s), and designing the optimum injection parameters. Both geological and petrophysical data have been used to create the geomechanical earth model for an oil prospect located at Farafra oasis in the Western Desert. This model defines the mechanical properties, pore pressure, and in-situ stresses of the different subsurface formations. Afterwards, a fully 3D fracture simulator has been used to simulate the fracture growth within the candidate injection zone at different injection scenarios. Additionally, the fracture simulator has assessed the containment of the created fracture within the candidate injection formation(s) due to the presence of stress barriers above and below the formation. Finally, the formation disposal capacity has been calculated for each of the injection scenarios using a stress increment model. The geomechanical earth model shows that there is a good candidate injection zone which is upper/lower bounded by stress barriers. More importantly, it is located deeper than the local fresh water aquifer and thus no contamination is expected to the fresh ground water. In addition, the possible candidate is not a hydrocarbon bearing formation. A 3D fracture simulator has been used to determine the optimum injection parameters such as: the injection flow rate, the volumetric solids concentration, the slurry rheology and the injection batch duration. These optimum parameters are defined to minimize the stress increment rate over the well life, which ensure the highest disposal capacity and to contain the fracture within the candidate injection formation. Guidelines to conduct waste slurry injection technique in a new oil prospect that is located within a sensitive environment as in the Western desert are presented in this study. Also, the study highlights that this technique is economic for disposal of the different oilfield waste types in an environmentally friendly fashion.

Carbon offset describes the environmental benefit from an initiative that avoids, reduces or removes greenhouse gases (GHGs) from the atmosphere. The Intergovernmental Panel on Climate Change has identified Carbon Dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O) as major constituent of the GHGs. Wastewater Treatment Facilities (WWTFs) among several other sectors is a neglected source for GHG emission. Considering the risk of rise in GHGs, United States along with other countries signed the Paris Agreement to respond to the global climate change threat in 2016. It is assessing projects to cut GHGs in exchange for emission credits that can be used to comply with goals they set under the United Nations pact. In order to curb the GHG emission by WWTFs, an innovative approach "Bioslurry Injection" (BSI) can be implemented to reduce the emission of the GHGs produced during the course of biological and chemical treatment of wastewater. The technology is inherited from the traditional drill cutting injection and Carbon sequestration technology implemented by the Oil and Gas industry since 1980's. The BSI operation has the ability to accept the feed from different treatment stages after the initial screening process to prepare the injection slurry and help in controlling the GHG emission at respective treatment stage along with managing the intake volume. The slurry can be prepared by mixing the treated biosolids with wastewater and injected into a pre-selected underground earth formation, where biosolids undergo anaerobic digestion and decompose into CO2 and CH4. An injection formation with sufficient capacity to accept the slurry is selected by conducting a detailed geomechanical and fracture simulation analyses. Along with the injection feasibility, the calculations of the amount of Carbon dioxide equivalent (CO2e) sequestrated underground by implementing BSI technique is presented in this paper. The sequestration of decomposed GHGs is an environmentally friendly activity that has proved to be economically beneficial due to its ability to earn carbon offsets. According to the new carbon law in the state of California the amount of CO2e eliminated from the atmosphere can be traded to earn carbon credits. TIRE facility through its ability to sequester and thus eliminate emission of the GHGs from the atmosphere can gain up to $1.5M worth of carbon credits per year providing both environmental and economic benefit. Also, low capital and operating cost for the BSI facility due to its compact surface requirement is an additional advantage along with reduced risk of spillage hazard when BSI facility is incorporated within the WWTF boundaries.

The injection of oil and gas wastes produced during the exploration and production phases have been proven to be an effective technique toward achieving zero discharge. However, several challenges are associated with the injection of slurry into an underground formation. The most common challenge during waste slurry injection (WSI) is the continuous loss of well injectivity due to poor engineering design of the injection parameters for most of the current existing WSI wells. For the WSI operation, near wellbore formation damage (including the fracture damage) will be formed by the injected solids. The real time injection monitoring of the ongoing operations is important to correct any operational mistake and adjust the injection parameters in order to ensure the well longevity. The paper discusses the importance of injection monitoring and steps necessary to maintain the injectivity and perform a healthy WSI operation. Three different case studies are presented to highlight the operational mistakes that caused a significant formation damage development in injectors in Eagle Ford, Haynesville, and Permian Basin shale plays. Certain guidelines depending on the monitoring results are provided in modifying the slurry rheology, pressure, injection strategy etc. that are helpful in maintaining the injectivity. The presented case studies show that the wells with good monitoring program maintained its injectivity during the course of its operation compared to the other wells that lost its injectivity sooner. The results from different case studies are used to prepare a set of guidelines that can be used to maintain the well injectivity and extend the well life. This paper discusses the techniques that will help in eliminating and avoiding the problems leading to formation damage and well plugging during the WSI operation.