Cement-formation Interface Research Articles

Study on the mechanism and controlling method for annulus pressure buildup problems in shale gas wells

The Annulus Pressure Buildup (APB) problems in shale gas wells is mainly caused by the crack at casing-cement interface. The stresses on casing-cement interface and cement-formation interface are calculated by the established model which the constrain of formation rock is considered. The elastic modulus of cement sheath has great effect on the stress on casing-cement and cement formation interface. The radial stress on interfaces changed linearly with fluid pressure. The cement rock is treated as a porous elastic material and the residual strain in cement sheath is mainly caused deformation or collapse of pore structure in the cement rock due to the large radial stress on interfaces. Ultimately, micro-annulus will be generated on the casing-cement interface due to the residual strain of cement sheath. High flexibility cement rock is proposed to decrease the radial stress on the interfaces which can reduce the residual strain of cement sheath. On the other hand, PABP is proposed to offset the decreased radial stress due to residual strain. A model for calculating the stress on interface by considering residual strain of cement sheath and PABP is established. The radial stress on the interfaces caused by PABP is quantitative calculated. The mechanism on how the method for solving APB problems in shale gas wells is clearly explained. The field application certificated the validity of method for solving the APB problems and it also proved the correctness of the calculation method.

Cased-hole reverse time migration imaging using ultrasonic pitch-catch measurement: Theory and synthetic case studies

Cement-bond evaluation is of great significance in oil/gas development, geothermal production, and CO2 storage. Advanced ultrasonic pitch-catch measurement exhibits poor performance in determining a cement-formation interface due to weak reflections from the cement-formation interface (third interface echo) in nonaxisymmetric complex ultrasonic environments. To deal with this issue, we use a reverse time migration (RTM) approach for ultrasonic pitch-catch measurements to image the cased-hole structure, especially for the cement-formation interface. To further enhance cased-hole RTM feasibility, a phase-shift interpolation technique is applied to reconstruct ultrasonic array waveforms from limited receivers in the pitch-catch measurement. Synthetic examples demonstrate that RTM is capable of imaging the cement-formation interface with a high resolution under various eccenterings of casings and tools. This study illustrates that small errors introduced by phase-shift interpolations do not greatly degrade the imaging result of RTM. Furthermore, tests for inclined cement-formation interfaces demonstrate that the RTM is able to recover the true position and geometry of the cement-formation interface when a smoothed velocity model is available. In addition, although RTM is sensitive to the velocity perturbation, it is possible to image the cased-hole structure by using a multistep strategy assuming that the position and thickness of the steel casing are unknown.

A deep learning workflow for weak reflection extraction in pitch-catch measurements in the cased hole

As a key technology to evaluate cement bonds in the cased hole, an advanced ultrasonic logging tool combines pulse-echo and pitch-catch measurements in which the latter one provides reflections from the cement-formation interface (called third-interface-echo [TIE]) to evaluate the bond condition and determine casing eccentering as well as cement velocity. However, the TIE would be weak and not easy to pick due to the eccentered tool and casing and it would overlap with the strong multiple reflections between the casing inner surface and the transducer-housing tool. We have developed a deep learning workflow to extract weak TIE from noisy data and to preserve its amplitude at the same time. First, we use synthetic waveforms from thousands of finite-difference simulations as initial training data sets to train a deep learning network, which is modified from a network in speech separation. Then, the trained model is used to predict the field data through an active-learning strategy. The improved network is further used to extract the weak TIEs, which are not easy to pick in the initial deep learning model. Finally, the TIE waves image is converted to a pseudovelocity image to obtain the minimum traveltime path by solving the eikonal equation. The shortest traveltime path is used as the TIE arrival time. In addition, a 3D visualization is used to display the borehole shape from the picked arrival time. The applications in synthetic data and data set from a calibration well illustrate a good performance of our workflow in which the weakest TIE extracted from the network can reach 50 dB compared to the maximum amplitude in the full waveform. The picked arrival times can be used to reconstruct a borehole shape.

Simulation study of cement plug micro-annulus in milling section of abandoned wells

When the integrity of the annular barrier outside the casing is degraded, parts of the casing in the abandoned well must be milled to place a permanent barrier. Considering the micro-annulus induced by accumulation fluid, this paper developed a 3D finite element model of cement plug in the milling section. Monte Carlo methods evaluated the fluid accumulation rate as a part of the model. The model simulated the micro-annulus propagation at the cement-formation interface under the fluid-driven force. The influence of milling position and reaming radius was analyzed. Meanwhile, the influence of the Poor Bonding Zone (PBZ) was analyzed based on a new method of simulating bonding quality. Simulation results show that the accumulation fluid affects the interface stress state and induces the micro-annulus. The initial stress of the interface is non-uniformly distributed under non-uniform in-situ stress, and the micro-annulus tends to expand along the axial direction. The selection of low Young's modulus, high Poisson's ratio, and low permeability formation region for milling is beneficial. The micro-annulus is highly sensitive to PBZ, and reducing the proportion of PBZ on the bonding face is significant in preventing barrier leakage. The results of this paper are essential for permanent barrier design and prevention of leakage.

Effects of the mechanical properties of a cement sheath and formation on the sealing integrity of the cement-formation interface in shallow water flow in deep water

The sealing integrity of cement sheaths is critical for the long-term stable and safe production of crude oil and natural gas. The temperature variation in wellbores may cause mechanical disturbances during production, causing the failure of the cement-formation interface (CFI) and sealing integrity. In this work, the cohesive zone method (CZM) was applied to study the effect of SWF caused by well-production disturbance on the CFI. Artificial simulation cores and traction-separation experiments were applied to acquire interface parameters required by the CZM. Based on ABAQUS, the effects of the elastic moduli and Poisson’s ratios of the cement sheath and formation and casing internal pressure on the initial failure pressure of the CFI were studied. The results showed that the initial failure pressure was important to ensure the integrity of the CFI, and once initial damage occurred in the CFI, the pressure driving the failure area to expand was much lower than the initial failure pressure. The elastic modulus and Poisson’s ratio of the shallow formation greatly influenced the initial failure of the CFI. The CFI was less likely to fail as the formation depth increased. Shallow water flow (SWF) had little effect on the cement sheath integrity after long-term curing. Furthermore, the simulation indicated that the elastic cement sheath contributed little to the resistance of the CFI to SWF.

An Experimental Study on the Reinforcement of Weakly-Consolidated Shallow Formation in Deep Water Using an Epoxy Resin-Based Fluid

The mechanical properties of Portland cement differ from the weakly consolidated shallow formation in deep water. This results in undesired abrupt changes in the compressive strength and elastic modulus at the cement–formation interface. In this study, a water-borne epoxy resin was applied as a strengthening material to reinforce the weakly consolidated shallow formation and protect the cement sheath from potential failure. The mechanical properties of the unconsolidated clay were tested, including their changes with increases in the temperature and curing time. In addition, the effects of the seawater, cement slurry alkaline filtrate, and saltwater drilling fluid were evaluated. As confirmed by the results, the strengthening fluid was excellent at reinforcing the unconsolidated clay, with a compressive strength of 2.49 MPa (after curing for 7 days), even at a dosage of 5%. A cement slurry filtrate with a high pH was suitable to produce the required strengthening of the formation, especially its early age strength. It should also be pointed out that the used fluid exhibited good compatibility with the saltwater drilling fluid and seawater behaved well as a diluent for the strengthening fluid.

Experimental investigation of the cementation and tensile properties of cement to formation interface considering surface irregularity and drilling mud residue

Cement sheath is an annular structure situated between casing and formation, which is designed to seal the formation and reinforce the borehole. However, owing to the surface irregularity and drilling mud residue, the interface between the cement sheath and the formation is one of the weakest parts for fluid leakage causing well integrity issues, which would also affect the reliability of the cement bond logs. To evaluate the cementation state and tensile properties of the cement-formation interface, rock-cement composite disc specimens are prepared, considering key factors such as lithology, interface irregularity, treatment of oil-based drilling mud contamination, and flushing fluid washing. Flushing efficiency of the drilling mud contaminated rock surface, interface cementation characteristic, referenced tensile strength, and tensile fracture morphology are acquired and analysed comparatively. Results show that (1) the flushing efficiencies of shale and sandstone are 74.1 ~ 61.9% and 52.4 ~ 28.4%, respectively, decreasing with the increase in surface irregularity. (2) The rock-cement interface gradually becomes poorly cemented as the surface cleanliness decreasing and the irregularity increasing. (3) Under the condition of drilling fluid contamination, there exists a transitional area at the cemented interface, where microcracks and pores are developed. (4) With the influence of drilling mud contamination, the referenced tensile strengths of shale-cement and sandstone-cement interfaces drop from 2.716 to 0.586 MPa and from 2.840 to 0.007 MPa, respectively. The effects of underground temperature and pressure environment are not particularly considered in this study and would be investigated systematically in future research.

Experimental study on modification of water-based filtercake to improve the bonding strength at the wellbore cement-formation interface

The objective of this experimental study is to improve the cementing bond quality of sandstone oil-gas well along the wellbore cement-formation interface (WCFI), so as to ensure long-term zonal isolation throughout the lifecycle of the well by using NSO solution as filtercake modifier which was developed in the laboratory. According to designed experimental method and API RP 10, the effectiveness of filtercake modifier (NSO) on the bonding strength at the WCFI was assessed by using designed simulated wellbore as sandstone formation. The experimental results indicated that the samples which were treated with NSO solution had higher bond strength over untreated samples. The strength generally increased with curing period as for treated samples, 0.198, 0.374, 0.433 and 0.473 MPa for 3, 7, 15, and 30 days respectively while for the untreated samples the bond strength were 0.050, 0.070, 0.81 and 0.100 MPa for the same period. The water-based filtercake modification techniques had significantly enhanced the bonding strength of WCFI by increasing rates above 296%. Improvement of bond strength to the treated sample was due to filtercake modification as a result of formation of cementitious material as revealed in FTIR spectral such as Calcium-Silicate-Hydrate (C–S–H) and other geopolymers like Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) and Sodium-Aluminium-Silicate-Hydrate (N-A-S-H)) along the interface which filled the existed pores hence reducing porosity hence high strength of bond. The low transmittance value for the NSO treated samples revealed that there were more cementitious materials existing at the WCFI which led to improvement of bonding strength as compared to the untreated samples. The lower/poor bond strength for the untreated samples is due to existence of untreated, thick water-based filtercake films at WCFI, which prevented the complete hydration process between rock grains and cement slurry components to make chemical binder of cement slurry material and formation.

Influence Laws for Hydraulic Sealing Capacity in Shale Gas Well Cementing

SummaryEnsuring the sealing integrity of cement sheaths used for shale gas wells during hydraulic fracturing processes has become a major challenge. The sustained casing pressure, strong temperature difference stress, and cyclic loading and unloading affect the safe long-term production of shale gas wells. In this paper, we propose a new hydraulic sealing capacity (HSC) evaluation system for cementing interfaces. Specifically, this study aimed at understanding the influence law and failure mechanism of the interface sealing of shale gas wells before hydraulic fracturing. The results showed that the HSC improved with an increase in the flushing time and velocity. The HSC of the cement-formation interface was likely to be compromised if the cement slurry was contaminated with a spacer and oil-based mud (OBM). When the cement slurry was mixed with more than 10% OBM, channels formed easily in the cement sheath body. Moreover, the preflush injection sequence of “flushing fluid + spacer + flushing fluid” significantly improved the HSC of the cement-formation interface. Based on the experimental results and field operation experience, we determined that the optimal flushing time and flushing displacement were 15–20 minutes and 1.8 m3/min, respectively. Finally, the microstructure and distribution characteristics of the cement-formation interface under different conditions were obtained by computed tomography (CT) analysis, which explains the formation and failure mechanism of the cement-formation interface HSC. The development of harmful pores (R > 1 mm) was the main factor affecting the HSC of the cement-formation interface. The number of harmful pores in cement-formation interface increased significantly after being polluted by OBM. Combined with the field operation experience, the prefluid injection sequence of “6 m3 flushing fluid + 25 m3 spacer fluid + 6 m3 fresh water” is adopted, and the displacement volume is 1.4–1.6 m3/min, and the cement slurry is injected 10–15 m3 more, which can greatly improve the HSC of the cement-formation interface. Our findings highlight the need for more explicit considerations regarding the impact of cementing technology and actual operation on the HSC of an interface under the requirements of efficient production and extended well life.

Experimental Study on the Compressive and Shear Mechanical Properties of Cement–Formation Interface Considering Surface Roughness and Drilling Mud Contamination

In a casing-cement sheath-formation system, the cement–formation interface is usually weakly cemented for the residual of drilling mud, in which a leakage path would easily form, threatening the safe operation of underground energy exploitation and storage. To evaluate the compressive and shear mechanical behavior of the cement–formation interface, cement–rock composite cylindrical specimens were prepared. Uniaxial and triaxial compression and direct shear tests were implemented. The flushing efficiency of the rock surface, compressive strength, interface incompatible deformation, parameters of shear strength, and morphology of shear failure surface were acquired and analyzed. Results show that the flushing efficiency of shale surface decreases from 76.7% to 64.2% with the surface roughness increasing from 0 to 2 mm. The flushing efficiency of sandstone is only 44.7%, remarkably lower than that of shale. With the stress condition transforming from uniaxial to triaxial compression, the feature of the stress–strain curves changes from elastic-brittle to elastoplastic, and the compressive strength increases from 20.6~60.1 MPa to 110~120 MPa. The cement part presents noteworthy plastic deformation and several micro shear fractures develop. There is incompatible deformation between cement and rock, which induces interface debonding for almost all the composite specimens. The internal friction angle and cohesive strength both decrease with the increase in pollution degree of drilling mud, and increase with the rise in surface roughness. The shear facture surface is not exactly the rock–cement interface, but usually manifests as a shear zone, in which the rock, cement, and interface all contribute to the final shear failure. The above findings would be valuable for the revealing of cement–formation interface failure mechanism.

Numerical analyses of coupled thermo-mechanical behaviors of cement sheath in geothermal wells

The stability of cement sheath under high temperature and high pressure is one of the most critical issues for the durability of geothermal well systems. In this study, a two-dimensional plane-strain finite element code was developed to investigate the coupled thermo-mechanical behaviors of the casing-cement-formation system. Different from previous linear elastic analyses, a thermoelasto-plastic constitutive model based on the thermodynamic theory was adopted for the cement sheath. It is shown that the finite element simulations using the proposed model provide a more accurate and realistic prediction of stress–strain responses of the cement sheath under high temperature. The results demonstrate that the radial stress concentration and the tensile strain concentration occur at both the cement–casing interface and the cement–formation interface, where the cement sheath is most likely to fail. High strength and low stiffness in the cement sheath and the formation are preferred for the integrity of the system. Both large thermal cycles and large differences between the internal fluid pressure and the external pressure should be avoided during operation. The new code is an alternative tool for guiding the geothermal well design. The finite element framework described herein is universal for other thermo-mechanical applications, such as energy foundations and energy tunnels.

An Integrated Approach to Study Cement-to-Formation Bonding

It is crucial to assess the bond strength of the cement–formation interface while developing novel cements for efficient zonal isolation. An integrated method is presented to investigate the failure mechanism in cement and formation rock under downhole reservoir temperature and pressure conditions using a triaxial experimental setup. The acoustic emission count, strain, and velocity data aid in inferring the fracture process that led to the failure of a specimen. Although most specimens investigated exhibit the three dominant events of compaction, multi-cracking, and sliding, there are variations in the basic structure of each specimen. Furthermore, the insight obtained about the internal structure of the specimen points to its strength and damage tolerance, both of which are vital requirements for bonding. This method can distinguish between a standard cement and modified cement very effectively and help in pairing the appropriate cement formulation for a formation rock.

Filter Cake Removal during the Cementing and Completion Stages in CO2 Storage Wells: Current Developments, Challenges, and Prospects

Carbon capture and storage (CCS) technology has become one of the most cost‐effective and promising ways to achieve global climate change mitigation goals. The CO2 storage capacity in depleted oil and gas reservoirs is currently the safest and most economical option. The long‐term sealing of the cement–formation interface in CO2 storage wells (CSW) is essential to avoid CO2 leakage. The filter cake easily affects the interfacial sealing ability, which is a thin impermeable layer formed by drilling fluid residue or solid particles remaining on the borehole wall due to permeable formation. Filter cake removal is essential for favorable cementation and production efficiency. This study highlights the current developments and the main challenges for oil‐ and water‐based mud filter cake removal during the cementing and completion process. Moreover, research ideas and recommendations for various types of filter cake removal are proposed to provide a reference for future work. This information helps deepen understanding with respect to the different filter cake removal options available in the CCS industry and provides a knowledge base that can facilitate the improvement of the cementing quality and production efficiency of existing systems to combat battle CSW safety and production efficiency problems.

Epoxy Resin-Based Cementing Fluid Produces a Low Elastic Modulus Cementing Fluid System and Enhances the Cement–Formation Interface

Epoxy Resin-Based Cementing Fluid Produces a Low Elastic Modulus Cementing Fluid System and Enhances the Cement–Formation Interface

Cement Sheath Integrity in Anisotropic Shale Formations: A Numerical Investigation

Cement sheath should provide zonal isolation and structural support during the full life cycle of a well. However, achieving long-term cement sheath integrity under complex geological and operational conditions, especially in bedding shales characterized by strong anisotropy, is still a great challenge. Thus, to better understand the effects of the anisotropy of shales on cement sheath integrity, this paper developed a 3D coupled thermal-hydro-mechanical model of the formation-cement-casing system. Stress generation and evolution within cement sheath are also considered in the modeling. The model is validated against analytical solutions and physical experimental results. Then, sensitivity analyses were performed to investigate the initial stress of cement sheath and shale anisotropy on cement sheath integrity. The results show that the anisotropy of Young’s modulus has a greater influence on cement sheath integrity compared to the anisotropy of Poisson’s ratio. Debonding between the cement sheath and formation can be easily generated due to the shale’s high anisotropy of Young’s modulus. The aperture of the microannulus along the cement interface varies with the angle between the wellbore axis and the bedding plane. The minimum microannulus is developed where the wellbore is parallel to the shale’s bedding planes. The results also indicate that initial stress generated in the cement sheath after its hardening is beneficial for the integrity of the cement-formation interface.

Study on the penetration of strengthening material for deep-water weakly consolidated shallow formation

Unformed-rock silt and sand are the main components of shallow formations in deep-water oil and gas wells. The formations are different from the perspective of mechanical performance of the cement sheath and often causes brittle failure. Improving the cement system or cement-formation interface strength is not sufficient to solve this problem. This study tested solid and liquid strengthening materials to increase the mechanical performance of weakly consolidated shallow formations and to minimize the performance difference with cement stone. The test of the groutability of superfine slag, cement, and epoxy resin indicated that waterborne epoxy resin system is the best choice. An annular simulation core was used to evaluate the penetration of the epoxy resin system. The simulation cementing experiment indicated that the viscosity of the ER (epoxy resin) slurry and the compression degree of the core negatively correlated with the permeate depth, while the grouting pressure exhibited positive correlation. The permeate depth can reach 11.8 mm under 0.1 MPa while the maximum was 21.7 mm at 0.4 MPa. A thin ER layer was formed between the cement sheath and the core after the ER slurry was cured, which increased the cement-formation interface strength by 22.18 %. Standard blocks showed that 5% of ER can increase the strength of unconsolidated clay to 2.17 MPa. SEM indicates that the ER filled part of the space between the particles of clay and consolidated them. The difference between standard blocks and core samples after treatment in SEM was low. The difference in mechanical performance between the cement stone and the weakly consolidated formation was narrowed after the formation was reinforced. • The groutability of solid and liquid strengthening material was evaluated. • The effect of grouting pressure, compress degree, and slurry viscosity on the permeate depth was studied. • The mechanism of epoxy resin to reinforce the weakly consolidated shallow formation and improved the cement-formation interface strength was revealed. • The mechanical properties between the cement sheath and the weakly consolidated formation were narrowed.

A Parametric Study for Radial Cracking in Cement Under Different Loading Events Based on the Stress Intensity Factor

AbstractCement is one of the primary barriers in a wellbore and critical to well integrity. Radial cracking is a pervasive failure mode in cement due to the temperature and pressure variation during drilling, completion, or production. This work presents a comprehensive analysis of radial cracking in cement under various loading events. The proposed model estimates the stress intensity factor and fracture surface displacement as indicators for crack propagation and opening, respectively, through a distributed dislocation technique. Three types of radial cracks, divided by their tips terminating at the casing–cement interface, inside cement, or at the cement–formation interface, are considered. Based on this model, we conduct a parametric study for radial cracking under typical loading events such as steam injection, CO2 injection, and high-pressure and high-temperature (HPHT) drilling. Results indicate that the crack near the casing–cement interface has an increased risk for steam injection and HPHT drilling, while all three types of radial cracks are destructive during CO2 injection. The thermal expansion coefficient of cement is a significant parameter for steam and CO2 injection wells. The fluid pressure and the cement’s thickness are crucial to radial cracking under HPHT conditions. Stiffer cement could promote crack opening for steam injection but prohibit the crack deformation for CO2 injection or HPHT wells. Thicker cement would accelerate radial cracking under the three loading events. These findings are helpful in designing cement to maintain long-term integrity.

Investigation of the interface cracks on the cement sheath stress in shale gas wells during hydraulic fracturing

Wellbore integrity problem induced by insufficient seal ability of the cement sheath has become a technical challenge of shale gas wells during hydraulic fracturing. In this paper, a new model has been established to characteristic the mechanics of the casing-cement interface (CCI) and the cement-formation interface (CFI) of the shale gas wells. In this model, the radial stress and the stress intensity factor has been analyzed to predict the prolongation of the initial cracks caused by perforation through comparison of the stress intensity factor and the interfacial fracture toughness of the CCI and CFI. In addition, the influence of the casing and cement parameters on the interfacial stress and the crack width of the CCI and CFI has been discussed in detail, and the optimal design of these parameters has been proposed according to the field data. Finally, the conclusions and some realistic suggestions have been put forward based on the discussion.

Pilot Test of pH Triggered Polymer Sealant for CO2 Storage

Wellbore integrity is a critical subject in oil and gas production and CO2 storage. Successful subsurface deposition of various fluids, such as CO2, depends on the integrity of the storage site. In a storage site, injection wells and pre-existing wells might leak due to over-pressurization, mechanical/chemical degradation, and/or a poor cement job, thus reducing the sealing capacity of the site. Wells that leak due to microannuli or cement fractures on the order of microns are difficult to seal with typical workover techniques. We tested a novel polymer gelant, originally developed for near borehole isolation, in a pilot experiment at Mont Terri, Switzerland to evaluate its performance in the aforementioned scenario. The polymer gel sealant was injected to seal a leaky wellbore drilled in the Opalinus Clay as a pilot test. The success of the pH-triggered polymer gel (sealant) in sealing cement fractures was previously demonstrated in laboratory coreflood experiments [1-3]. pH-sensitive microgels viscosify upon neutralization in contact with alkaline cement to become highly swollen gels with substantial yield stress that can block fluid flow. The leaky wellbore setup was prepared by heating-cooling cycles to induce leakage pathways in the cased and cemented wellbore. The leakage pathways are a combination of fractures in the cement and microannuli at the cement-formation interface. The exact nature of these leakage pathways can be determined by over-coring at the end of the experiment life. We used polyacrylic acid polymer (sealant) to seal these intervals. The process comprises of three stages: (1) injection of a chelating agent as the preflush to ensure a favorable environment for the polymer gel, (2) injection of polymer solution, and (3) shut-in for the polymer gelation. Then, we evaluated the short-/long-term performance of the sealant in withholding the injected fluids (formation brine and CO2 gas). The novel sealant was successfully deployed to seal the small aperture pathways of the borehole at the pilot test. We conducted performance tests using formation brine and CO2 gas to put differential pressure on the polymer gel seal. Pressure and flow rate at the specific interval were monitored during and after injection of brine and CO2. Results of performance tests after polymer injection were compared against those in the absence of the sealant. Several short-term (4 min) constant-pressure tests at different pressure levels were performed using formation brine, and no significant injection flow rate (rates were below 0.3 ml/min) was observed. The result shows more than a ten-fold drop in the injection rate compared to the case without the sealant. The polymer gel showed compressible behavior at the beginning of the short-term performance tests. Our long-term (1-week) test shows even less injectivity (~ 0.15 ml/min) after polymer gelation. The CO2 performance test shows only 3 bar pressure dissipation overnight after injection compared to an abrupt loss of CO2 pressure in the absence of polymer gel. Sealant shows good performance even in the presence of CO2 gas with high diffusivity and acidity. Pilot test of our novel sealant proves its competency to mitigate wellbore leakage through fractured cement or debonded microannuli, where other remedy techniques are seldom effective. The effectiveness of the sealing process was successfully tested in the high-alkaline wellbore environment of formation brine in contact with cement. The results to date are encouraging and will be further analyzed once over-coring of the wellbore containing the cemented annulus occurs. The results are useful to understand the complexities of the cement/wellbore interface and adjust the sealant/process to sustain the dynamic geochemical environment of the wellbore.

Evaluation of azimuth cement bond quality based on the arcuate phased array acoustic receiver station

Cement bond quality is a crucial parameter in oil production, and acoustic logging is among the main methods of evaluating this property. By analyzing the characteristics of casing and formation waves, the cement bond quality of the casing–cement interface (interface I) and cement–formation interface (interface II) can be evaluated. However, the use of both monopole sources and receivers render the evaluation of the azimuth and angle range of cement channeling difficult using conventional acoustic logging tools. Herein, we developed an improved azimuthally acoustic bond tool (AABT 2.0) comprising a monopole acoustic radiator and arcuate phased array (APA) acoustic receiver stations with enhanced azimuth resolution capability. AABT 2.0 can determine the azimuth and angle range of cement channeling and improve the resolution of azimuth measurement. We studied these factors through numerical simulation and physical experiments. Numerical simulation results show that the azimuth of cement channeling can be determined by measuring the amplitude of the casing wave's head wave in multiple azimuths received by the APA acoustic receiver stations in a casing well. Compared with individual-reception mode, APA acoustic receiver stations with the scanning-reception mode can both determine the azimuth of cement channeling more accurately and confirm the angle range of cement channeling. Data processing results from experimental wells show that AABT 2.0 can evaluate the cement bond quality of interface I with a high azimuth resolution in the circumferential and axial directions, through the amplitude imaging display of the casing wave's head wave. The reliability of AABT 2.0 and the accuracy of our measurement results are verified through comparison with results from an ultrasonic imaging logging tool and information concerning the well condition.