Detail of GB/T 41029-2021

Introduction of GB/T 41029-2021

1 Scope This document establishes the requirements for well abandonment operating procedures and information management in offshore oil and gas exploration and development operations. This document applies to oil and gas operations in the internal waters of the People's Republic of China. Territorial waters, contiguous zone, exclusive economic zone, continental shelf and other waters under the jurisdiction of the People's Republic of China for oil and gas exploration and development operations. It may also be used for operations in waters outside the PRC. 2 Normative references The contents of the following documents constitute essential provisions of this document through the normative references in the text. Among them, note the date of the reference documents, only the date of the corresponding version applicable to this document; do not note the date of the reference documents, its latest version (including all the revision of the list) applicable to this document. GB/T19139 Test methods for oil well cements 3 Terminology and definitions The following terms and definitions apply to this document. 3.1 well residuum on seabed An object left on the seabed (or bottom of a body of water in the case of inland waters) above the mud surface near the wellhead after well abandonment operations have been completed. 3.2 abnormal well An oil and gas well that meets one or more of the following conditions, depending on its final state prior to disposal: a) Gas wells and wells with a gas to oil ratio exceeding 350 (m'/m2 ) in standard conditions; b) Wells with corrosive fluids such as H2S or CO2 in the formation and which are susceptible to corrosion after abandonment; c) Wells with a maximum formation pore pressure equivalent density greater than 1.30 g/cm'. 4 General requirements, principles and procedures for well abandonment operations 4.1 General requirements 4.1.1 Prior to well abandonment operations. The integrity of the well pad shall be assessed and remedial measures shall be taken if the integrity requirements are not met. 4.1.2 After well abandonment operations, the formation and other permeable formations shall be effectively sealed so that the formation fluids between different pressure regimes cannot interfere with each other and there shall be at least two levels of barrier to ensure that there is no leakage of formation fluids to the subsea mud surface. 4.1.3 Casing and annular voids that have not achieved effective cement containment should not be used as a barrier for permanent well abandonment. 4.1.4 The first cement plug in the shot hole section, in the casing above the bare eye or above the tail pipe suspender shall be probed for cement plug topping and pressure tested to pass. 4.1.5 The last cement plug in the permanent abandonment well shall be not less than 50 m in length and the top surface of the plug shall be located 4 m to 30 m below the mud surface of the seabed. 4.1.6 When a cement plug is used to seal the flow channel between the oil, gas and water permeable layers in a permanently abandoned well, the length of the individual cement plug shall not be less than 50 m. In the case of oil, gas and water permeable layers in large-slope wells and horizontal wells, the length of the cement plug shall not be less than 50 m. The vertical height of the cement plug above the top of the water permeable layer shall not be less than 30 m. 4.1.7 When permanently abandoning a well in a water town within the territorial sea, all casing, piles, etc. shall be cut 4 m deeper than the mud surface of the sea floor. 4.2 Temporary well abandonment operation procedures 4.2.1 Completion of exploratory wells by casing or tailbore injection 4.2.1.1 Cement plugs or drillable bridge plugs shall be injected and cemented within 15 m above the top of each set of injection sections and poured to seal the oil and gas layer. A drillable bridge plug shall be placed within 15 m above the top hydrocarbon layer, pressure tested and a cement plug of not less than 30 m in length shall be placed on top of it. When the layer spacing is short, the cement shall be poured on top of the bridge plug when using the drillable bridge plug for sealing. 4.2.1.2 For special wells, the length of the cement plug shall not be less than 30 m when sealing between oil and gas formations with cement injection; when the layer spacing is short, the top of the plug shall be poured with cement when sealing with a drillable bridge plug. A drillable plug should be placed within 15 m above the top oil and gas layer. Pass the test pressure and inject a cement plug of not less than 50 m in length on the bridge plug, probe the top surface of the cement plug and pass the test pressure. 4.2.1.3 In the inner casing with effective cement seal in the annulus, inject a cement plug of not less than 50 m in length upwards (the length of the cement plug in this location should not be less than 100 m for special wells) and probe the top surface of the cement plug. The cement plug should be located close to the surface casing shoe. 4.2.1.4 When keeping the wellhead above the water surface, after completing the last - abandoned well cement plugging operation, take anti-corrosion and anti-freeze mopping measures above the cement plug as needed; when keeping the wellhead below the water surface, a wellhead cap or protective cap for the mudline suspension should be installed, and anti-corrosion measures can be taken as needed. Anti-hydrate and other measures. 4.2.1.5 abandonment of the well end, should be set up wellhead markers and safety protection facilities. 4.2.1.6 At the end of the temporary well abandonment, documentation of the well abandonment operation shall be filed and reported to the competent administrative authorities. 4.2.2 Exploration wells completed with bare eye or bare eye screen tubing 4.2.2.1 Depending on well conditions, fill the bare-hole section or screen tubing with completion or drilling fluid to protect the reservoir. 4.2.2.2 Seal a drillable bridge plug within 30m above the top packer of the casing shoe or screen tubing in the bare hole and test the plug with a cement plug of not less than 30m in length. Special wells should be filled with a cement plug of not less than 50m in length. The top surface of the cement plug shall be explored and tested for pressure. 4.2.2.3 In the inner casing with an effective cement seal in the annulus, inject a cement plug of not less than 50m in length upwards, preferably close to the surface casing shoe, and probe the top surface of the cement plug. Special wells shall have a drillable bridge plug seated at this location, pressure tested and filled with a cement plug of not less than 50 m in length. 4.2.2.4 Follow up operations shall be completed in accordance with 4.2.1.4.4.2.1.5.4.2.1.6. 4.2.3 Development wells 4.2.3.1 Wells drilled in abnormally pressurised sections, or wells not shot after cementing under casing (or tail pipe) in oil and gas sections shall be fully pressure tested and the wellhead shall be fitted with a wellhead device that can monitor wellhead pressure and provide pressure access. A retrievable bridge plug shall be installed and pressure tested at the subsea wellhead. 4.2.3.2 Injected wells or bare-hole completion wells, it is recommended that the production tubing column is lowered, a recovery tree is installed and the wellhead device is pressure tested, or that at least two formation fluid control barriers are achieved by placing a bridge plug, injecting a cement plug and installing a temporary wellhead. Refer to 4.2.1.4.2.2 for other well conditions. 4.2.3.3 Follow up operations are to be completed in accordance with 4.2.1.4.4.2.1.5 and 4.2.1.6. 4.3 Protocols for permanent well abandonment operations 4.3.1 Casing or tailbore completion of exploratory wells 4.3.1.1 Inter-stratigraphic sealing of oil and gas formations The top surface of the cement plug should not be lower than 30m above the shot hole section. If the layer spacing is short, the cement plug can be injected continuously to seal multiple layers; for special wells, it is advisable to put a bridge plug between layers and continue to inject cement plugs upwards to seal them. 4.3.1.2 Plugging of top oil and gas layers 4.3.1.2.1 The cement return height of the uppermost oil and gas layer should not be lower than 50 m above the top of the injection section, and the top surface of the cement plug should be explored and pressure tested; or the bridge plug should be placed within 15 m above the top of the uppermost injection section. Pass the test pressure, and inject a cement plug of not less than 50 m in length on the bridge plug. 4.3.1.2.2 In special wells, it is advisable to place a cement squeeze packer within 15 m above the top injection section and to squeeze cement into the oil and gas reservoir by means of a test squeeze injection or intermittent cement squeeze, the amount of which shall be sufficient to seal the injection section or the maximum squeeze pressure to reach the original formation rupture pressure in that section. After cementing, a cement plug of not less than 50 m in length shall be injected into the cement packer, the top surface of the plug shall be probed and the plug shall be pressure tested. 4.3.1.3 Tail pipe hangers. Grading hoop blocking Inject a cement plug with a length of not less than 60 m upwards at a point approximately 30 m below the tail pipe suspension and grading hoop. 4.3.1.4 Plugging of the upper pipe section 4.3.1.4.1 In the inner casing near the shoe depth of the surface casing and with an effective cement seal in the annulus, inject a cement plug of not less than 50 m in length upwards, probe the top surface of the plug and confirm. 4.3.1.4.2 Special wells shall be sealed with a bridge plug in the inner casing near the shoe depth of the surface casing and with an effective cement seal in the annulus, and after passing the pressure test, a cement plug of not less than 50 m in length shall be injected into it and the top surface of the plug shall be inspected and confirmed. 4.3.1.5 Upper casing recovery Cut and recover the casing and casing head. See 4.1.7 for the required depth of cut for the last layer of casing. 4.3.1.6 Casing cutout sealing Cement plugs are to be injected upwards at least 30 m below the cut-out position of each layer of casing that has been cut, with the cement plugs covering upwards to at least 30 m above the cut-out position. 4.3.1.7 Subsea Wellhead removal In accordance with the relevant regulations of the administrative authority of the marine area. 4.3.1.8 Documentation Upon completion of the permanent abandonment of the well, information shall be submitted for record in accordance with the requirements of the competent administrative authority. 4.3.2 Exploration wells completed with bare eye or bare eye screen tubing 4.3.2.1 Inter-layer sealing of oil and gas formations 4.3.2.1.1 In exposed borehole sections, the permeable layers of oil, gas and water shall be fully sealed by drilling a cement plug at least 50 m above them to seal the permeable layers of oil, gas and water to prevent interflow or outflow from the seafloor. If there is no oil, gas or water in the exposed section of the borehole, a cement plug is drilled in the last - . At least 30 m of cement plugs should be placed below and above the last - . 4.3.2.1.2 In bare borehole sieve tube sections, if well conditions permit, seal the bare borehole section by blocking it, or by sealing a cement squeeze packer within 30m above the top sieve tube packer, using a test squeeze injection. Intermittent cement squeezing is used to squeeze cement into permeable layers of oil, gas and water. 4.3.2.2 Plugging of the top oil and gas layer 4.3.2.2.1 Inject cement plug upwards near 30m below the top packer of the casing shoe or sieve pipe in the upper bare eye, the top surface of the cement plug should be 50m above the top packer of the casing shoe or sieve pipe, probe the top surface of the cement plug and test pressure to pass. 4.3.2.3 Follow-up operations Follow up operations shall be completed in accordance with 4.3.1.3 to 4.3.1.8. 4.3.3 Development wells where the tubular column in the well can be recovered 4.3.3.1 Tubular column recovery The well is pressurised and the downhole production tubulars are recovered. 4.3.3.2 Inter-layer sealing of bare-hole sections Cement plugs should be used to seal the flow path between oil, gas and water permeable layers in a bare-hole section or in a bare-hole screened tubular section, with a single plug length of not less than 50m. When sealing oil, gas and water layers with cement plugs, they shall be covered from 30 m below the bottom of the blocked oil, gas and water layer upwards to not less than 30 m above the top of the blocked layer. 4.3.3.3 Inter-layer sealing of the shot hole section 4.3.3.3.1 Cement plugs shall be injected in sections from not less than 30 m below the bottom of each group of injection sections upwards, with the top surface of the cement plugs being not less than 30 m above the top of each group of injection sections. 4.3.3.3.2 When mining or injecting with a layered pipe column but with short layer spacing, the layered pipe column may be closed. The top of the cement plug should be no less than 30m above the top of the blocked section. 4.3.3.4 Plugging of the top oil and gas layer 4.3.3.4.1 The cement return height for sealing the top oil, gas and water layer shall be not less than 50m above the top of the layer to be sealed, and the top surface of the cement plug shall be explored and pressure tested to pass. 4.3.3.4.2 Special wells should be sealed within 30m above the top of the oil and gas formation, the top casing shoe of the naked eye or the top packer of the screen pipe -. Only the cement squeeze packer should be used to squeeze cement into the formation using the test squeeze injection and intermittent squeeze cement method. After the cementing process is completed, a cement plug of not less than 50 m in length shall be injected into the cementing packer, the top surface of the cement plug shall be probed and tested for pressure. 4.3.3.5 Follow-up operations Follow up operations are to be completed in accordance with 4.3.1.3 to 4.3.1.8. 4.3.4 Development wells where the production tubular column in the well cannot be fully recovered 4.4 Other well abandonment principles and requirements 4.4.1 Production well sections that are no longer in use should be abandoned in the same manner as a permanently abandoned well. 4.4.2 Abandoned well cement shall be tested and qualified in accordance with the requirements of GB/T19139. 4.4.3 The quality of the seating and sealing of the plug shall be ensured in the lower plug section and the cementing quality of the cement to the casing wall shall be ensured in the cemented section. 4.4.4 Before and after the floating drilling unit has completed the well abandonment operation, it is advisable to launch a remotely operated vehicle (ROV) to inspect and photograph the area around the wellhead (within a radius of 30m) and to map the remains of the wellhead on the sea floor. 4.4.5 Underwater inspection, photography and mapping of the subsea wellhead may be carried out when necessary after the well abandonment operation is completed by the jack-up or fixed drilling unit. 5 Well abandonment information and reporting 5.1 Well abandonment plan preparation 5.1.1 Exploratory well design The exploratory well drilling design should include an abandonment design. 5.1.2 Overall oil and gas field development programme The overall oil and gas field development programme shall include the well abandonment programme. 5.1.3 Well abandonment operation plan A well abandonment plan shall be prepared and submitted to the competent administrative authority prior to operation. The plan shall include: a) An assessment of the safety risks associated with well abandonment or wellhead removal. b) The plan for abandoning the well or removing the wellhead remnants, operating procedures, schedule, well fluid properties, etc. 5.2 Well abandonment report preparation and collection 5.2.1 Collect and collate information on well abandonment operations and prepare an abandonment operation report. 5.2.2 The well abandonment report should include the following: a) The name of the field/block and the geographical location of the sea area; b) Well name and well location coordinates; c) Water depth and elevation of the rotary core; d) A summary of the well abandonment process, including the dates of abandonment, etc; e) Well structure and casing dimensions for each layer and actual depth of penetration; d) Cementing cement return height and pressure test data for each outer casing level: g) Depth of each formation and the original pressure of the formation, section and depth of the shot hole; h) Number of bridge plugs inserted, depth of insertion and pressure test data; i) Number of cement plugs. Depth, length, density and pressure test data; j) depth of casing cut in each layer; k) Completion diagram of abandonment and debris removal operations; l) Schematic diagram of the final well structure for the abandonment operation. 5.2.3 The abandonment report should be included and maintained in its entirety as part of the well history.

Contents of GB/T 41029-2021

Foreword 1 Scope 2 Normative references 3 Terms and definitions 4 General requirements, principles and protocols for well abandonment operations 5 Well abandonment information and reports bibliography