CO 2 Well Integrity and Wellbore Monitoring

Transcription

1 Oct CSLF Workshop Porto Alegre, Brazil CO 2 Well Integrity and Wellbore Monitoring Andrew Duguid

2 Why Worry About Wellbore Integrity 2 CO 2 Volumes The volume of CO 2 is so large that there will need to be thousands of injection and monitoring wells and the injected CO 2 will interact with existing wells CO 2 Properties Aggressive nature of CO 2 combined with its density may increase the risk of leakage Wellbore Material Properties Typical wellbore materials are susceptible to degradation under typical CO 2 sequestration conditions Wellbore Construction Practices Poor wellbore construction practices can lead to increased risk of leakage

3 Size of the problem 3 Currently the misbalance in the carbon cycle is about 3.1GtC/Yr If we wanted to inject enough to balance the carbon cycle right now it would take almost 11,500 Sleipner sized projects (not accounting for future emissions growth) Or an increase in NEW CO 2 use in EOR projects by a factor of 300

4 Size of the problem 4 One wedge = 25GtC (91.7GtCO 2 ) over 50 years 1GtC/Yr Pacala and Socolow, 2004 Estimates of storage capacity range from 184 to 245 GtC for oil and gas fields and 273 to 2700 GtC for deep saline formations Assuming a wedge scenario in 50 years one wedge will have filled between 5 and 0.9 % of the available space for geologic sequestration We probably have plenty of space

5 Why Wells Are Important 5 Strong Overlap On Highly Prospective Sedimentary Basins IPCC SRCCS, 2005

6 Possible storage leakage scenario 6 LEAKAGE CONFINING LAYER INJECTION WELL CO 2 BRINE ABANDONED SALINE AQUIFER WELL

7 Typical abandoned oil well 7 Surface casing and cement Plug at surface Uncemented zone Mud, water, or open casing Production casing and cement Plug in production zone

8 Potential avenues for leakage 8 E Well casing A LEGEND Cement Formation Drilling mud Well casing Open casing D B Migrating CO 2 C

9 Typical well cement composition 9 Unhydrated Phase Percent 3CaO SiO CaO SiO CaO Al 2 O 3 5 4CaO Al 2 O 3 Fe 3 O 3 12 Hydrated Phase Abbreviation Percent Ca 3 Si 2 O 7 4H 2 O C S H Ca(OH) 2 CH (3CaO Al 2 O 3 CaSO 4 12H 2 O) AFm CaO (Al,Fe 2 O 3 ) 13H 2 O AFt Data from Nelson, 1990

10 Cement degradation reactions 10 CO 2 dissociation CO 2 + H 2 O H 2 CO 3 * H + + HCO 3 2H + + CO 3 2 Cement dissolution Ca(OH) 2 (s) + 2H + + CO 3 2 CaCO 3 (s) + 2H 2 O Ca 3 Si 2 O 7 H 4H 2 O(s) + 2H + + CO 3 2 CaCO 3 (s) + SiO x OH x (s) Ca(OH) 2 (s) + H + + HCO 3 CaCO 3 (s) + 2H 2 O Ca 3 Si 2 O 7 H 4H 2 O(s) + H + + HCO 3 CaCO 3 (s) + SiO x OH x (s) Calcium carbonate dissolution CO 2 + H 2 O + CaCO 3 (s) Ca HCO 3 2H + + CaCO 3 (s) CO 2 + Ca 2+ + H 2 O

11 Reactions At The Cement Rock Interface Lab 11 Sandstone cement at ph 3 and 20 C Limestone cement at ph 5 and 20 C

12 Reactions At The Cement Rock Interface Field 12 SACROC Field Cement Carey et al. 2006

13 CO 2 Resistant Cement 13 Cements for remediation and construction of new wells can still be portland based. CO 2 resistant portland cements have been used and are currently available. Some CO 2 resistant cements work by reducing the amount of calcium hydroxide (CH) and increasing the amount of calcium silica hydrate (C S H). CSH is more resistant to CO 2 attach than CH. Additives such as pozzolans provide additional silicon to create C S H. Additives such as bentonite which require a large increase in the water to cement (W/C) ratio should be avoided. High W/C can lead to accelerated cement degradation

14 CO 2 Resistant Cement 14 Class G Cement CO 2 Resistant Cement Barlet Gouédard, 2006

15 Well Construction 15 Assuming that a well has sufficient zonal isolation CO 2 and carbonic acid will not have pathways for flow the cement in the wells should last a sufficient amount of time A Well constructed well maybe the best way to lower the potential for leakage The high ph of cement means that if there is no pathway for CO 2 or brine to reach a steel casing then the steel should be protected from degradation Placement defects fluid dynamics Channels Pockets or strings of bypassed drilling mud Mud films Increase of fluid volume, further reduction of cement thickness The use of centralizers in during cementing will reduce chances of creating these types of defects Gas migration during cement hydration may cause channels Driven by a drop in cement pore pressure during hydration Placement design and system selection

16 Tools Used on Recent Well Integrity Surveys 16 Multifinger Caliper Log (PMIT) Reservoir Saturation Tool (RST) Accelerator Porosity Sonde (APS) Natural Gamma Ray Spectroscopy Tool (NGT) Ultrasonic Imaging Tool (USIT) Isolation Scanner Sonic Scanner Cement Bond Tool (CBT) Cased Hole Dynamic Tester (CHDT) Modular Sidewall Coring Tool (MSCT)

17 Multifinger Caliper Measurements 17 Measurements provide 360 degree view of the condition of the inside of the casing Non destructive Can be used in casings between 1 ¾ to 13 3/8 in diameter Only provide information on the inside of the casing

18 Sonic Logging Cement Bond Logging Measurements provide information on casing cement and cement formation bonds Bond index provides quantitative information on cement to casing bond Variable density log provides qualitative information on the casing cement and cement formation bonds 18 Non destructive Measurements are averaged for the circumference and do not provide information on specific pathways Reasons for poor attenuation (poor bond) can be ambiguous. Should be run along with an ultrasonic logging tool to gain fullest picture of cement integrity

19 Ultrasonic Logging Measurements provide a 360 degree view well and provide information on the casing surface, casing thickness, casing cement bond, cement condition, and cementformation bond 19 Very sensitive to the condition of the borehole fluid Should be used in conjunction with a sonic log to provide best overall picture of well integrity Non destructive Transducer Casing Cement Mud Formation Echo amplitude (Internal casing condition) Transit time Thickness Cement Impedance Internal radius

20 Cased Hole Mobility Testing Measurements provide the actual, in situ, mobility (permeability) of the cement and formation at a point at a specific depth Multiple measurements can be made moving deeper into the side of the well 20 Measurements give good results in high mobility zones but the sensitivity of the instrument and our the ability to quantify low mobility zones is still under investigation Somewhat destructive Casing is repaired but the hole drilled in the cement / formation is not repaired

21 Cased Hole Fluid Testing and Sampling 21 In situ estimate of gas, oil, and water fractions of the formation fluid based on optical analysis of the formation fluid Collection of samples for further laboratory analysis Run in conjunction with cased hole mobility tool, so not additional hole through the casing and formation is required Years of reliable use in old wells

22 Cased Hole Sidewall Coring 22 Side wall cores allow for the physical sampling of the casing, the cement, and the formation Only method to physically examine the casing cement and cement formation Interfaces in existing wells Field samples are important because to date work by Kutchko et al.[2007], Duguid [2006], and Barlet Gouédard et al. [2006] have not tested cement under realistic field conditions for long periods of time Will leave a ~1 inch hole in the side of the well for each core taken that may require remediation if the well is not going to be plugged and abandoned

23 Sidewall Core Characterization Optical microscopy Permeability Density EPMA characterization SEM 23 X ray map X ray diffraction

24 Recommendations 24 Take into account all of the possible leakage pathways that may exist within the well Be cognizant that the best overall estimate of a well s integrity comes from taking different types of measurements Multifinger caliper Ultrasonic Sidewall coring E Well casing A Ultrasonic Cased hole mobility Sidewall coring Ultrasonic Sonic Sidewall coring D B Ultrasonic Sonic Sidewall coring C

25 Recommendations 25 Do logging sequentially to minimize the number of measurements that are needed if the well does not show good integrity Multifinger caliper Sonic and Ultrasonic Cased Hole Mobility and Fluid Testing Sidewall Coring At a minimum run the non destructive measurements Make physical measurements if the well is to be used as part of a group of representative wells in a storage site

26 Questions?