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Results
Chemo-mechanical Permeability Evolution In Wellbore-cement Fractures Exposed to Carbon-dioxide-rich Brines
Walsh, S.D.C. (Lawrence Livermore National Laboratory) | Du Frane, W.L. (Lawrence Livermore National Laboratory) | Sholokhova, Y. (Lawrence Livermore National Laboratory) | Settgast, R. (Lawrence Livermore National Laboratory) | Johnson, S.M. (Lawrence Livermore National Laboratory) | Carroll, S.A. (Lawrence Livermore National Laboratory)
ABSTRACT: Fractures in wellbore cement and at the cement-host rock interface are potential leakage pathways for long-term carbon sequestration sites. Portland cement exposed to carbon-dioxide-rich brine undergoes a series of diffusion-limited reactions that form distinctive reaction fronts adjacent to the cement surface. This paper outlines a joint experimental and numerical modeling effort investigating the formation of these reaction fronts and their impact on fracture transmissivity. Prepared by LLNL under Contract DE-AC52-07NA27344. 1. INTRODUCTION Fractures in wellbore cement and at the cement-host rock interface have been identified as potential leakage pathways for carbon dioxide in long-term sequestration sites [1-5]. In the presence of acidic carbon-dioxide-rich brines, the alkaline Portland cement degrades - causing distinctive layers of reacted material to form adjacent to the cement surface. To explain the formation of the reaction layers, Kutchko and co-workers [4,5] proposed a three stage mechanism for the degradation of Portland cement in the presence of carbon-dioxide rich brines: 1) Portland cement is largely comprised of calcium-silicate hydrate (CSH) and Portlandite (calcium hydroxide or CH) crystals. When the brine comes into contact with the cement, calcium leaches from the calcium hydroxide crystals. 2) Next the dissolved calcium reacts with the carbonic acid in the brine, precipitating calcium carbonate. 3) The calcium carbonate initially protects the CSH from the brine. However, once the acidic brine depletes the calcium carbonate, the CSH dissolves – leaving a high porosity amorphous silicate region with low material strength. As a consequence of these diffusion-limited reactions, the cement-brine boundary becomes divided into distinct regions separated by thin fronts where the reactions take place. Predicting the effect of these regions on fracture transmissivity is non-trivial, as the changes induced in the cement composition affect material strength and, consequently, the geometry of the fracture surface.
- Geology > Geological Subdiscipline > Geomechanics (0.70)
- Geology > Mineral > Silicate (0.44)
ABSTRACT: The Effective stress coefficient is a measure of how chalk grains are connected with each other. The stiffness of chalk may decrease if the amount of contact cements between the grains decreases, which may lead to an increase of the effective stress coefficient. We performed CO2 injection in chalk, as this process could affect the grain contact cement. If this happens, the effective stress at the grain contacts in a reservoir will change according to the effective stress principle of Biot. In a p'-q space for failure analysis, we observed that a higher effective stress coefficient reduces the elastic region and vice versa. However, as the effective stress working on the rock decreases with increased effective stress coefficient, the reduction of elastic region will have less effect on pore collapse strength if we consider the change in the effective stress coefficient. This finding will help estimate a more precise failure strength of chalk during changed stress state and under the influence of chemically reactive fluids during production of hydrocarbon and geological storage CO2. 1. INTRODUCTION Hydrocarbon reservoirs in chalk in the North Sea are sensitive to the changes that may occur during oil and gas production [1-3]. Failure of chalk could occur either due to an increase in effective stress caused by decrease in pore pressure or to a weakening of the chalk which may be caused by mechanical and chemical processes e.g. related to enhanced oil recovery by waterflooding or CO2 injection. Prediction of failure strength under changed stress state resulting from a particular production process is therefore necessary for designing future production strategies and reservoir management. The effective stress in a hydrocarbon reservoir typically increases during primary production of oil and gas or may decrease during waterflooding due to increased pore pressure.
- Europe > Denmark > North Sea (0.68)
- North America > United States > Texas (0.47)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Economic Geology > Petroleum Geology (0.54)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Europe > United Kingdom > North Sea > Central North Sea > Utsira High > PL 006 > Ekofisk Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > Block 2/8 > Valhall Field > Tor Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > Block 2/8 > Valhall Field > Hod Formation (0.99)
- (4 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Experimental Study On the Tensile Strength Weakening of Mudstone In Leaching Process of Bedded Salt Cavern
Yang, Chunhe (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Shi, Xilin (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Li, Yinping (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) | Yang, Juan (School of Materials & Engineering, Wuhan Institute of Technology) | Wei, Donghou (Petrochina Beijing Gas Pipeline Corporation Limited)
ABSTRACT: The existence of indissolvable muddy interbeds leads to many adverse effects for building salt cavern storages by solution mining. It is an urgent technical problem that how to forecast and control the collapse of indissolvable interbed in the salt cavern leaching process. Some experiments are carried out in order to reveal the tensile strength weakening discipline of interbed mudstone immersed in brine. The test results show that the lower the brine concentration is or the longer the immersed time is, the more obvious the weakening degree of the mudstone strength will be. The mudstone in bedded salt rock contains mainly clay mineral and also some dissolvable salt grains. The solution of salt grains and the softening and expansion of clay mineral are implied to be the key factors relative to the mudstone strength weakening, and the two factors promote each other during weakening process. It is also showed that mudstone samples with different salt content rates behave different weakening disciplines: immersed in brine with concentration close to field brine concentration, the tensile strength of mudstone samples with low salt content rate are weakened lightly and slowly; the samples with middle salt content rates are weakened obviously when immersed in middle concentration brine, and the solution of salt grains and the softening and expansion of clay mineral play a key role in strength weakening of mudstone; immersed in unsaturated brine, the samples with high salt content rate weaken quickly, and the primary reason is the failure of the material framework caused by solution of salt grains. 1. INTRODUCTION Deep salt deposits are the ideal places for oil or gas storage [1, 2]. The existence of indissolvable muddy intercalation leads to many adverse effects in leaching process of bedded salt cavern.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.84)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (1.00)
- Geology > Mineral (1.00)
Experimental Study of Portland Cement/Rock Interface In Relation to Wellbore Stability For Carbon Capture And Storage (CCS)
Agbasimalo, N. (Craft & Hawkins Department of Petroleum Engineering, Louisiana State University) | Radonjic, M. (Craft & Hawkins Department of Petroleum Engineering, Louisiana State University)
ABSTRACT: Primary cementing is carried out during the drilling and completions of wells and the main objective is to provide zonal isolation. For effective cementing, the cement should completely displace the drilling mud (water-clay mixture). In practice, this is never achieved as some of the mud is not displaced and remains in the wellbore. This study investigates the effect of the residual mud on the hydraulic conductivity of the cement-formation interface. Flow-through experiments were conducted at 14.48 MPa (2100 psi) overburden pressure with cement-rock composite cores and brine at a flow rate of 1 ml/min. The cement-rock composite cores had 0% and 10% clay-rich fluid contamination respectively. The pressure drop across the composite cores was recorded throughout the flow-through experiments. Extensive micro-structural characterization of the cement-rock interface was carried out before and after the flow-through experiments. Higher pH values were recorded for the effluent brine from the mud contaminated core and the higher values indicate increased leaching of Ca2+. Micro-CT imaging revealed that the contaminated composite core possessed higher porosity at the interface zone. This shows that clay contamination of cement-rock interface degrades the interface zone and can provide a pathway for injected CO2 to escape from the intended storage zone. 1. INTRODUCTION One of the most promising technologies for controlling the amount of greenhouse gases in the atmosphere is large scale geological sequestration of CO2 [1, 2]. A key aspect of CO2 sequestration is ensuring that the sequestered CO2 stays within the intended storage zone permanently. The fact that more than 8000 wells in the Gulf of Mexico currently exhibit sustained casing pressure highlights the importance of investigations into cement-rock bond issues [6, 7]. Poor rock-cement bond is usually caused by poor primary cementing which includes inadequate mud displacement.
- Research Report > New Finding (0.50)
- Research Report > Experimental Study (0.40)
- Geology > Geological Subdiscipline > Geomechanics (0.89)
- Geology > Mineral > Silicate (0.75)
Image-based Evaluation of the Effect of CO2-Rich Brine On the Preexisting Fracture System Within Wellbore Cement Under Dynamic Flowthrough Conditions
Ozyurtkan, Mustafa Hakan (Petroleum and Natural Gas Engineering Department, Faculty of Mines, Istanbul Technical University) | Detwiler, Russell (Civil and Environmental Engineering Department, The Henry Samueli School of Engineering, University of California) | Radonjic, Mileva (Craft and Hawkins Petroleum Engineering Department, Louisiana State University)
ABSTRACT: The effect of greenhouse gas CO2 on global warming has motivated numerous studies and projects around the world, which investigate new technology named Carbon Capture and Storage (CCS). Effective implementation of CCS technology will require containment of injected CO2 into subsurface geological formations over hundreds of years. The performance of structural seals overlying reservoirs targeted for CO2 storage will rely upon the integrity of well-bore cements in active and abandoned wells subjected to fluids rich in CO2. Micro fractures within the well-bore cement and micro-annulus at the casingcement and formation-cement may lead to seepage of CO2 to the surface and/or fresh water aquifers. Thus, understanding CO2- induced changes to the imperfections in the cement matrix is vital for safe and effective implementation of CCS and the impact such changes can have on the overall hydraulic conductivity of a wellbore system. This paper presents an experimental study that depicts changes of cement’s internal structure due to the interaction with acidic brine through a system of purposefully induced fractures within the cement matrix. The reported study is unique in that it employs advanced imaging analyses to quantify CO2- induced alteration of well-bore cements. Furthermore, a complementary high-resolution surface profilometry allowed quantification of changes of the roughness of fracture walls and their impact on the fracture aperture as a result of cement-acidic brine interaction over 100 days. 1. INTRODUCTION CCS projects require capturing carbon dioxide from large point sources such as fossil fuel power plants and other manufacturing processes that produce CO2 and storing it below the earth’s surface for hundreds of years. The long-term containment of injected gas is a critical component for effective CCS, requiring that potential pathways for leakage during early stages of injection be identified, investigated and risk assessment performed.
- North America > United States > Louisiana (0.29)
- North America > United States > Texas (0.28)
- North America > United States > California (0.28)
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.34)
- Geology > Mineral (0.72)
- Geology > Geological Subdiscipline > Geomechanics (0.67)
Solids Production In Chalk
Papamichos, E. (Aristotle Univ of Thessaloniki, Greece and SINTEF Petroleum Research) | Berntsen, A.N. (SINTEF Petroleum Research) | Cerasi, P. (SINTEF Petroleum Research) | Vandycke, S. (Mons University) | Baele, J.-M. (Mons University) | Fuh, G.-F. (ConocoPhillips) | Han, G. (Hess, Houston) | Kristiansen, T.G. (BP Norway)
ABSTRACT: Open hole or perforated completions in chalk fields are studied experimentally and are simulated theoretically to obtain an insight on the mechanisms involved in their stability. Hollow cylinder experiments with flow on Lixhe chalk have identified two mechanisms of chalk production: (a) Breakout failure through shear band development and pore collapse, (b) Tensile failure and destabilization due to high drawdown. Solids production results for chalk are presented where solids production by tensile failure is more often observed in water-flooded areas. Depending on the conditions it can be a rather violent phenomenon. The analysis presents the critical drawdown and depletion conditions for the two failure modes and demonstrates the influence of brine sensitivity on the results. 1. INTRODUCTION Open hole or perforated completions in chalk fields are difficult to design due to the various competing stabilizing and destabilizing factors. Analysis of such completions has shown that the problem consists of a rather complex combination of multiphase flow and geomechanics [1]. Chalk influx tests on hollow cylinder or cavity specimens with single or multiphase (oil/brine) flow are critical for the understanding of the important destabilizing mechanisms in chalk. Hollow cylinder tests with or without flow are often used to obtain the borehole/perforation strength of reservoir sandstones and their sand production potential (e.g. [2-4]). However, only limited studies have been carried out on chalk where Raaen and Renlie [5] have presented results from three hollow cylinder core tests. There are important differences between the high porosity pure chalks and reservoir sandstones. Such are the high porosity of chalks coupled with their low permeability due to the fine particle size. Chalks exhibit also pore collapse, that is, a sudden loss of pore volume at stresses relevant for hydrocarbon production, which results in substantial volumetric compaction.
- North America > United States (0.69)
- Europe > Norway (0.48)
- Research Report > Experimental Study (0.68)
- Research Report > New Finding (0.46)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.55)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.54)
- Europe > United Kingdom > North Sea > Valhall Formation (0.89)
- Europe > Norway > North Sea > Valhall Formation (0.89)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Tor Formation (0.89)
- (2 more...)
- Well Completion > Completion Installation and Operations (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Geochemical Controls On Fracture Evolution In Carbon Sequestration
Fitts, J.P. (Dept. of Civil & Environmental Engineering, Princeton University) | Ellis, B.R. (Dept. of Civil & Environmental Engineering, Princeton University) | Deng, H. (Dept. of Civil & Environmental Engineering, Princeton University) | Peters, C.A. (Dept. of Civil & Environmental Engineering, Princeton University)
ABSTRACT: Stored supercritical CO2 will acidify native brines in deep saline aquifers and promote mineral dissolution within the storage formation resulting in varying degrees of calcite saturation. Injection overpressure will force these reactive brines into existing and induced fractures in overlying caprock formations. We present examples from our experimental efforts to understand how these fluids might alter fracture geometry and leakage pathway permeability, with the ultimate goal of predicting caprock integrity. We use mineral-specific imaging analysis to correlate changes in fracture geometry with spatial maps of dissolution and precipitation. Synchrotron-based x-ray spectroscopy and diffraction imaging of thin section sub-samples of the cores from the flow-thru experiments are used to connect mineral-specific dissolution and precipitation processes with the geometric changes in fracture aperture observed with CT images. Results of µXRF, µXANES and µXRD analyses reveal that preferential calcite dissolution and the spatial distribution of relatively insoluble dolomite and silicate minerals produced the non-uniform aperture widening. These results clearly point to the need for predictive models of caprock integrity to consider coupled geochemical processes, mineralogical characterizations, and geometric alterations of flow paths. 1. INTRODUCTION One of the most important challenges to predicting the long-term integrity of caprock formations overlying geologic CO2 storage reservoirs is evaluating how much CO2 will flow through caprock fractures, potentially damaging other subsurface resources and eventually escaping to the atmosphere. In addition to studies that quantify the spatial distribution and permeability of existing and induced fractures and faults, mounting experimental evidence suggests that predictive models of caprock integrity need to consider how CO2-acidified brines will react with fracture walls and thereby change the permeability of these flow paths with time. This paper contributes to the growing body of experimental work aimed at identifying the conditions of fluid chemistry and caprock mineralogy that will result in fracture erosion.
- Geology > Mineral > Silicate (0.69)
- Geology > Geological Subdiscipline > Geomechanics (0.68)
- Geology > Geological Subdiscipline > Geochemistry (0.61)
- (2 more...)
ABSTRACT: The dichotomy between the fact that the potassium (K+) ion is well known to be a preferred additive in drilling and completion fluids, and the widely held belief that osmosis plays an important role in the clay/shale-fluid interaction problem has been intriguing for several years. This ion dependency alone challenges the osmotic theory of shale stabilization, and over the last two decades a vast amount of research to examine the existence of swelling, and the feasibility of osmosis under wellbore conditions has led to additional doubt. A review of that research is summarized in this paper, and a number of factors that have not been satisfactorily addressed, but are important to the discussion are examined. These factors include a reassessment of laboratory results that promulgated swelling, a simple assessment of whether the accepted osmotic process could create pressure imbalances that would cause dewatering, a compilation of basic ion properties that are important to the analysis, an examination into why there is ion specificity in the manner and results of the ion transfer process (and consequently why K+ is preferable over other cations) and finally a presentation of likely reasons for the stabilizing impact of ion interactions with clay surfaces. Additionally, the ion selectivity structures present in cell walls were found to be an interesting analog to the shale-fluid interactions problem, and their functions will be presented as well. 1. INTRODUCTION / BACKGROUND It has long been recognized that exposure of drilling and reservoir treatment fluids to rock formations can have negative impacts on wellbore stability and reservoir production capabilities. This paper strives to examine and evaluate the state-of-the-art in shale-fluid nteraction analyses and theories, and to introduce (and in most cases reintroduce) some basic concepts that are a major part of the shale-fluid interactions discussion.
- Europe (1.00)
- Asia (1.00)
- North America > United States > Texas (0.93)