An Overview of Injection Design

Abstract

Abstract Recent advances in research have significantly improved the understanding of formation damage induced from injection operations. Specific measures, such as injector half life, and models for predicting injectivity decline have been developed to assist engineers in designing optimum injection operations. During a similar time frame, Underground Injection Control (UIC) regulations formulated under the Safe Drinking Water Act (SDWA) have been enacted and have served as a catalyst for changes in downhole injection design and operation of injection wells. This paper provides a concise overview of the state of injection design. The paper includes a review of fundamental injection design, presents research results in formation damage due to brine injection, and discusses the downhole design(s) currently required by law under 40 CFR (US Code of Federal Regulations). Introduction Formation injectivity and injectivity decline due to formation damage from inject brines, are principal concerns in waterflood (Class II) injection design. From the operators standpoint, formation damage is the principal concern because increasing damage reduces injectivity, and can affect the longevity of the injection well. Regulatory compliance aspects of the injection operation and the environmental implications of the wellbore design are also of paramount importance. These issues determine whether an injector can be permitted, the maximum injection pressure which can be sustained, and any risks which the injector may pose to overlying sources of drinking water. Design Considerations of Waterflood (Class II) Injection Wells. The design of a Class II injection well must considerFormation injectivity and injection well testingFormation damage, injectivity decline and filteringRegulatory considerations for injection design Selection of tubulars, injection pumps and surface facilities such as brine filters is made on the basis of design parameters related to these issues. Formation Injectivity and Injection Well Testing. Formation injectivity is one of the first parameters determined in injection design. The formation's ability to accept the injected brine will govern the tubulars and surface injection requirements. Injectivity also can affect the selection of the injection pattern and the number of injection wells per producing well in pressure maintenance and waterfloodng operations. Determination of the base formation injectivity also provides a baseline observation from which predictions of the long term injectivity of the well can be made. All of these considerations are important to the economic success of injection projects. Well tesing techniques have been employed in injection wells to determine reservoir parameters such as injectivity, in-situ permeability and skin factor, formation parting pressure and fracture extension pressure. These techniques include injectivity tests, falloff tests and step-rate tests.