API RP 90-2006 pdf download.Annular Casing Pressure Management for Offshore Wells.
1 General 1.1 SCOPE This Recommended Practice is intended to serve as a guide for managing annular casing pressure in offshore wells. Although the prevention of annular casing pressure is very important, it is beyond the scope of this document. Prevention of annular casing pressure is planned to be addressed in API RP 65, Part 2. The remediation of wells because of sustained casing pressure is also beyond the scope of this document and is planned to be included in API RP 65, Part 3. This guide is meant to be used for offshore wells that exhibit annular casing pressure, including thermal casing pressure, sustained casing pressure (SCP) and operator- imposed pressure. This Recommended Practice covers monitoring, diagnostic testing, the establishment of a maximum allowable wellhead operat- ing pressure (MAWOP) and documentation of annular casing pressure for the various types of wells that occur offshore. Included also is a discussion of risk assessment methodologies that can be used for the evaluation of individual well situations where the annular casing pressure is not within the MAWOP guidelines. This Recommended Practice recognizes that annular casing pressure results in various levels of risk to the safety of personnel, property and the environment. The level of risk presented by annular casing pressure depends on many factors, including the design of the well and the source of the annular casing pressure. This Recommended Practice provides guidelines in which a broad range of casing annuli that exhibit annular pressure can be managed in a routine fashion while maintaining an acceptable level of risk. Annular pressures that do not conform to the guidelines in this Recommended Practice may still have an acceptable level of risk, but they need to be evaluated on a case-by-case basis.
1.2 DOCUMENT ORGANIZATION Regarding annular casing pressure, this Recommended Practice has general information that is applicable to all offshore well types. For each of the well types covered by this Recommended Practice, fixed platform wells, subsea wells, hybrid wells and mudline suspension wells, a section for each well type has been provided in which complete information is given for that well type. While in many cases this is redundant information, it allows the user of the Recommended Practice to go to the section for the applicable well type and review all of the information in one section. 1.3 DEFINITIONS 1.3.1 “A” Annulus: The annulus designation between the production tubing and production casing. 1.3.2 ambient pressure: Pressure external to the wellhead. In the case of a surface wellhead, it would be zero psig. In the case of a subsea wellhead, it would be equal to the hydrostatic pressure of seawater at the depth of the subsea wellhead in psig. 1.3.3 “B” Annulus: The annulus designation between the production casing and next outer casing. The letter designation continues in sequence for each and every outer annular space encountered between casing strings up to and including the surface casing and conductor casing strings.
1.3.4 barrier elements: One or several dependent objects, i.e., packers, tubing, or casing, preventing formation fluids from flowing unintentionally into another formation or to the surface. 1.3.5 conductor casing: Provides structural support for the well, wellhead and completion equipment, and often provides hole stability for initial drilling operations. This casing string is not designed for pressure containment, but upon completion of the well, it may have a casing head; therefore, it may be capable of containing low annular pressures. This casing is set prior to encountering any hydrocarbons at a depth where the fracture gradient will allow for an increase in mud density and is cemented to the surface or mudline. For subsea and hybrid wells, the low pressure subsea wellhead is normally installed on this casing string. 1.3.6 diagnostic testing: Tests or techniques performed to evaluate the existence of annular casing pressure, and in some cases, to attempt to determine the source of the annular casing pressure. Included are bleed-down/build-up tests, evaluation of flu- ids and volumes from bleed-down tests, evaluation of real-time accessible pressure data, production logs, operational observa- tions, etc. 1.3.7 drive/jet pipe: Supports unconsolidated deposits and provides hole stability for initial drilling operations. This is nor- mally the first string set and provides no pressure containment. This string can also provide structural support to the well system. 1.3.8 fixed platform wells: Wells completed with a surface wellhead and a surface tree on a fixed platform. All of the casing strings are tied back to the surface wellhead. 1.3.9 hybrid wells: Wells drilled with a subsea wellhead and completed with a surface casing head, a surface tubing head, a surface tubing hanger, and a surface christmas tree.