Evaluating Sustainable Annulus Pressure (SAP) in Sour Wells and the Possible Causes to Avoid Recurrence
Mahmoud Farag April 28, 2015 Abu Dhabi, UAE
Outlines What is Sustainable Annulus Pressure (SAP)? Risk Associated with SAP SAP Sources SAP - US Regulations SAP - Norway Regulations Prevention Methods Diagnostic Methods Remediation Methods Conclusions
What is Sustainable Annulus Pressure (SAP)? ďƒ˜
Definition:
SAP is defined as a pressure in any well annulus
that is measurable at the wellhead and rebuilds when bled down, not caused solely by temperature fluctuations or imposed by the operator (e.g., gas-lift pressure, gas- or waterinjection pressure).
Society of Petroleum Engineers (SPE) Webinar on Wellbore Integrity Paul Hopman March 27, 2013
Risk Associated with SAP
The most serious problems have resulted from tubing leak When the resulting pressure on the production casing causes a failure of the production casing, the outcomes can be catastrophic The outer casing strings could also fail, resulting in an underground blowout SAP represents a potential risk of losing hydrocarbon reserves and polluting aquifers and sea with hydrocarbons
Photograph of Blowout Resulting from incident of SAP
Mud cake leaks
Casing leak
SAP Sources Well-head leak
APB
CSG Burst Tensile cracks in cement caused by temperature & pressure cycles
Tubing leak Payne - SPE Forum
Low pressure sand
Corrosion Damage High pressure sand
Underground blowout Channel caused by flow after cementing
Micro-annulus caused by casing contraction
Figure from “A Review of Sustained Annulus Pressure (SAP) Occurring on the OCS� by Bourgoyne et al (March 2000)
Harper - KDHE
SAP – US Regulations ďƒ˜
According to US Minerals Management Service (MMS) regulations, diagnostic testing is required in any well exhibiting sustainable annulus pressure (SAP). The departure (waiver) decisions are solely based on the results from annulus pressure diagnostic tests ďƒ˜ Results of the test determine if immediate SAP removal could be temporarily waived (departure permit) and continuing operation of the well permitted
SAP – Norway Regulations Norsok D-10:
Pressures in all accessible annuli shall be monitored and maintained within min and max operational pressure limits to verify that the integrity status of well barriers is known at all times A-annulus pressure in all wells and B-annulus pressure in multi purpose and gas lifted wells shall be monitored through continuous recording Subsea wells, the B-annulus designed to withstand thermal pressure build up, or have an acceptable pressure management system
SAP - Platform versus Subsea wellheads
Prevention Methods Preventive Practices for Well Construction & Production: Well Planning & Design Detection & Diagnostics: SAP Sources and Pathways SAP Barriers: Mechanical, Cement, Rock & Chemical Sealants Thermal APB (Annular Pressure Build-Up): Avoidance, Prevention & Venting Well Integrity Testing
Well Planning & Design Review of the existing wells design, drilling & completion operations, problems & lesson learnt Well Design issues: Change in casing setting depth Material selection Maximum load concept which includes: • • • • •
Burst load design Collapse load design Buckling & wellhead load design Biaxial analysis Triaxial analysis
Example of the Stability Force and Wellhead Loads Design Calculations (Paper 73 – SPE Conference Houston, May 2005)
Example of the Stability Force and Wellhead Loads Design Calculations (Paper 73 – SPE Conference Houston, May 2005)
Cementing Issues In order to avoid the annular gas leakage problem in the early stage of life cycle of the well it was recommended to achieve optimum cementing. Gas migration during & after the cementing job and the presence of micro annuli are the principle causes for the poor WI of the production casing cementing sheath which allows the migration of hydrocarbon to the surface. These aspects has not been considered at the well design stage to mitigate “B” annulus pressures in critical wells.
Best Cementing Practices To avoid gas migration and the forming of micro annular spaces it is recommended to take into consideration the following: Careful planning of mud properties Gas pockets encountered while drilling should be fully depleted prior to cementing Hole size ; 1.5 to 2 inches > CSG or LNR size Cement quality & weight Turbulent flow for mud removal
Best Cementing Practices (Cont’d) The cement should, if operationally possible, be displaced with a fluid of the same density Waiting time; to avoid changes in density, dilution, settling, water separation and gas cutting Losses should always be cured and gas presence eliminated prior to starting cementing External casing packer should be run just above the gas bearing zone Casing pipe centralization
Cement Quality Evaluation
Pressure tests: Shoe bond test, casing integrity test, dry test, communication test, only dynamic tests …but can damage casing to cement bond ( Micro Annulus ) …if performed after cement setting
Electric-line Logging: CBL/VDL , Ultra-Sonic logs Other logs: temperature (cement top if recorded within a few hours), noise, Oxygen activation, etc.
Cement job quality assessment sheet
Cement Shoe Bond Integrity Test
A cement job quality assessment sheet
Diagnostic Methods
Maximum Allowable Wellhead Operating Pressure (MAWOP) Calculation Flow Testing & Sampling Well Log Analysis Pressure Bleed-Down Performance Pressure Build-Up Performance Upper & Lower Diagnostic Thresholds (DTs) Wellhead & Tubular Pressure Testing Data Record & Documentation
Maximum Allowable Wellhead Operating Pressure (MAWOP) MAWOP from API RP 90 for an annulus is the lesser of the following: • 50% of the MIYP of the casing being evaluated; or • 80% of the MIYP of the next outer casing; or • 75% of the MCP of the inner tubular pipe body • The outermost pressure-containing casing MAWOP can not exceed 30% of its MIYP
MAWOP Example API RP 90 Annulus Prod Tubing "A" "B" "C" "D"
3.5", 12.9#, L-80 7 5/8",39#, Q-125 9 5/8", 53.5#, Q-125 13 3/8", 68#, K-55 18 5/8", 87.5#, K-55
MIYP Collapse PSIG PSIG 15,000 15,310 14,340 12,060 12,390 8,440 3,450 1,950 2,250 630
50% MIYP PSIG 7,170 6,195 1,725 1,125
75% Collapse PSIG 11,483 9,045 6,330 1,463
80% MIYP PSIG
MWOP PSIG N/A 7,170 9,912 2,760 2,760 1,725 1,800 675
% MIYP
50% 22% 50% 30%
Flow Testing & Sampling ďƒ˜The weight & composition of the fluid that flows from the well during pressure bleedoff operations can yield valuable information regarding the density of the annulus fluid and the source of the behind pipe influx of fluids
Well Log Analysis
Noise Log Temperature Log Cement Evaluation Logs Corrosion Evaluation Log Down Hole Camera Production Logging…etc.
Pressure Bleed-Down Performance ďƒ˜ One of the best opportunities to obtain information about the annular volume, gas content and channel/micro-annulus flow capacity. This operation is normally performed through a fix sized (0.5-in) needle valve and the liquid / Gas recovered is also measured. ďƒ˜ Process requires either recording the casing pressure once per hour or use of a data acquisition system or chart recorder during a pressure bleed-down test.
Pressure Bleed-Down Performance (Cont’d) The following data shall be recorded; WHP, Ann.-A & B pressures prior & after bleeding HP connection size, bleeding time Type of return fluid Ann.-A & B pressures build up value & time on hourly basis (for at least 48 hours)
Pressure Bleed-Down Testing Patterns
Pressure Bleed-Down Testing Patterns (Cont’d)
Pressure Build-Up Performance ďƒ˜ Also
requires the pressure build-up period to be monitored after bleeding off SAP. The rate of pressure build-up provides additional information about the size and possibly the location of the leak. The pressure build-up test is especially important when the SAP cannot be bled to zero through a (0.5-inch) needle valve.
Pressure Build-Up Testing Patterns
Pressure Build-Up Testing Patterns (Cont’d)
Pressure Build-Up Testing Patterns (Cont’d)
Upper & Lower Diagnostic Thresholds (DTs) Practically speaking, when blowing down or topping up any annulus, a compromise final pressure somewhere between the upper and lower limits should be attained. For blowing down : Too high a pressure means you will need to blow down extremely often Too low a pressure and one could aggravate the leak due to the increased pressure differential. Similar arguments apply to topping up
MINAP
Annulus Pressure Management - Triggers & Working Pressure
Wellhead & Tubular Pressure Testing Wellhead,
tubing and production casing leaks can often be identified by pressure testing Pressure test procedures can be used to supplement the diagnostic bleed-down test Pressure testing of wellhead seals is generally performed after SAP has been bled down
Data Record & Documentation
Routine WHP & Annuli Pressure Readings from Well A-5
Remediation Methods ďƒ˜ Rig-Less ď ą Bleed
Methods:
& Lubricate; A combination of bleeding off pressure and injecting a sealing/killing fluid either at the wellhead or at depth through flexible tubing inserted into the annulus (CARS)
Remediation Methods (Cont’d)
Remediation Methods (Cont’d) Rig
Methods:
Cement Squeeze Operations;
May have failed due to the inability to place sufficient barriers in the affected annulus
Remediation Methods (Cont’d) ď ą
Termination of the Inner Casing;
Consists of three base operations: 1- Cut and pull casing 2- Casing clean-out 3- Pressure isolation of the inner casing stub and annulus
The Cut and Pull Operation Illustrating the Cement & Mechanical Isolation of the Terminated Casing Stub
Remediation Methods (Cont’d) ď ą
Section Milling ;
Consists of five base steps: 1- Section milling 2- Preparation for pressure isolation of lower casing stub 3- Pressure isolation of lower casing stub 4- Preparation for pressure isolation of upper casing stub 5- Pressure isolation of upper casing stub
The Section Milling Operations
Conclusions
SAP was widespread in approximately 35% of wells worldwide Eliminating of the SAP problem in new wells was achieved by adjusting some aspects of the well design, improving some aspects of the cementing operation and introducing tighter QC of cementing Detailed diagnostic testing was recommended to identify the cause of the problem and establish the optimum route for the remediation of the problem Pressures in all accessible annuli shall be monitored and maintained within min and max operational pressure limits to verify that the integrity status of well barriers is known at all times
Questions?