Syahrir Ridha

Wellbore Failure During Water-Alternating-Gas Injection by Use of Flow-Stress Coupling Method

Accurate evaluation of failure pressure is crucial in the design of injection wells. Besides, in-situ stresses play an important role in obtaining the results. Pressure and rock stresses are related together as the role of effective-stress theorem. In fact, pressure changes with stress alteration caused by change in porosity and permeability. Therefore, it should be obtained with the coupling method. Moreover, to calculate pressure, temperature, and stress in the fully coupling method, a huge matrix should be solved, and it takes long processing time to implement it. Therefore, this study developed a wellbore geomechanical model for stability during injection by use of the iterative coupling method. The processing speed was enhanced in this study because the parameters were calculated separately. The parameters of pressure, temperature, saturation, and stress were obtained for the multiphase-flow condition with numerical modeling. Furthermore, in this study, the finite-difference method (FDM) had been used to solve pressure, temperature, and saturation, whereas the finite-volume method (FVM) was applied to solve the wellbore stress. On top of that, the iterative coupling method was used to improve the accuracy of the stress results. As a result, a correction of approximately 20 psi (0.14 MPa) was noted for pressure in relation to stress, which is 1 psi (6.89 kPa). Moreover, the Drucker-Prager failure criterion was used to model the fracturing on the basis of the stress results. Other than that, sensitivity analysis on horizontal maximum (o-H) and minimum (o-h) stresses showed that by increasing O-H, the maximum injection pressures to avoid fracturing had been reduced, whereas in the case for O-h, an increment was observed. Copyright

Development of Stress Model near the Wellbore Using an Iterative Coupling Method

AbstractWater-alternating-gas (WAG) injection is increasingly applied globally as the effective enhanced oil recovery (EOR) method in oil wells. High injection pressure or low injection temperature could lead to wellbore failure. The rock stress around the wellbore is a function of the wellbore pressure and temperature, and it should be precisely determined to avoid wellbore failure. This study aimed to develop a wellbore geomechanical model for WAG injection using an iterative coupling method. The parameters of pressure, temperature, saturation, and stress were obtained for the multiphase flow condition using mathematical modeling. The finite-difference method was used to solve pressure, temperature, and saturation, and the finite-volume method was used to solve the rock stresses. Because the values for flow and rock stresses are related by the role of effective stress, the pressure is the key parameter to determine the stress. However, pressure changes with stress because of the change in porosity and p...

Investigation on Mixed Oil-Cement for Wellbore Integrity Using Acoustic Velocity

Oilwell cementing is part of completing a well prior to production. As a casing is installed after a section of the well is drilled, cement is pumped downhole. Reservoir fluid such as oil which may encroach into the wellbore due to naturally fractured or unconsolidated formation would mix with the cement pumped downhole. Recent studies have shown that the presence of oil affect cement quality to an extent where the cement compressive strength is greatly reduced. Early detection of possible oil contamination into cement may prevent well integrity problem. With intense application of acoustic principle into wellbore, however, not many references available to detect the presence of oil in cement system using this principle. This study investigates whether acoustic waves can detect oil in cement. Class G cement is mixed with both water and brine where crude oil is then added to the mixture. The resulting slurry were cured using High Pressure High Temperature (HPHT) curing chamber at 120°C and 4,000 psi for 24 hours and is then cored into 1-inch cylinder. SonicViewer-SX is used to propagate acoustic waves through the core sample where the transit time is recorded and analyzed. It is found that oil can be detected in cement using acoustic waves since oil-filled samples have slower P-waves and S-waves velocities than cement-filled samples. The case is also proven when water is replaced by brine as the mixing fluid which oil-filled samples have lower P-waves and S-waves velocities to that of cement-filled samples.

Thickening Time Compatibility of Geopolymer Cement for Drilling Application

This paper investigates the composition of geopolymer cement for thickening time under elevated temperature and pressure. Geopolymer based-cement becoming popular in construction industries because of its improved properties either chemically and physically as compared to Ordinary Portland Cement (OPC). At the same time, replacement of OPC with geopolymer cement able to eliminate CO2 emission due to calcination burning process. However, applications of geopolymer cement to oil and gas industry for cementing job are not well recorded. Fly ash based geopolymer cement with different percentages of slag from 0% to 10% were mixed using sodium hydroxide and sodium silicate as alkali activators. Density, fluid loss and compressive strengths were determined. The sample were cured at 3,000 psi and 65°C for 24 hours. Results show that the addition of slag reduces the thickening time from 30 minutes to just only 18 minutes with almost 40% reduction in time. In terms of density and compressive strength, an increment of slag is directly proportional as the value increased from 14.3 ppg to 15.0 ppg for density and 1,120 psi to 2,155 psi for compressive strength. For fluid loss test, increment of slag results in decrement of fluid loss from 0.64 ml to just only 0.38 ml.

Wellbore stability model based on iterative coupling method in water alternating gas injection

AbstractEnsuring wellbore integrity is the most important factor in injection well design. The water alternating gas (WAG) injection is increasingly applied globally as the effective enhanced oil recovery (EOR) method in oil wells. High injection pressure or low injection temperature could lead to compressive wellbore failure. The rock stress around the wellbore is a function of the wellbore fluid flow and it should be precisely determined to avoid the wellbore failure. The purpose of this study is to propose a method to ensure the stability of the wellbore for the WAG process using iterative coupling method. The parameters of pressures, temperature, saturations and stresses are obtained for the multiphase flow condition using mathematical modeling. In this study, finite difference method is used to solve pressure, temperature and saturations; and finite volume method is acquired to solve the rock stresses. Iterative coupling method is employed to improve the accuracy of the results. This study introduces improved iterative coupling method between flow and stress models to reduce the processing time of obtaining corrected stress and failure results. Wellbore stability model is developed to determine the maximum pressure values, which lead to wellbore failure in WAG injection process for some different boundary conditions.

Prediction of interface conductivity of cement slurry during early hydration considering the effect of curing temperature and pressure

Electrical conductivity measurements have been widely used in characterizing the cementitious materials. In mature stages, the influence of interface conductivity to the overall conduction was relatively small. However, its contribution during early hydration is still questionable. This paper calculated the interface conductivity during the first 24 hrs of hydration at elevated temperature and pressure up to 65°C and 3000 psi. The effect of elevated temperature to conductivity measurement is successfully corrected. Johnson equation is employed to predict the interface conductivity of pore-solid particles. The microstructural parameters that are used in the equation are estimated from the proposed particle expansion model. These calculation outcomes have a good agreement compared to the MIP measurements. The results showed that the interface conductivity grew slightly with the progress of drying. Its contribution to the bulk conductivity is relatively very small of about factor 6 in orders of magnitude. Hence, the influence of interface conductivity to the overall conduction might be disregarded during cements early hydration.

Conductivity dispersion characteristic of cement slurry during early hydration

Electrical conductivity has been increasingly used for material characterization in the form of dispersion characteristic. However, the application of this method to the cement slurry is limited. This paper investigates the influence of water to cement ratio and degree of hydration to the dispersion characteristic of cement slurry during 24 hrs of hydration. The magnitude and frequency effect are used to describe the conductivity dispersion characteristic. It is observed that the magnitude of conductivity dispersion increases with the reduction in water content and pore volume. During initial hydration, the dispersion characteristic appears in the minimum value and raises as hydration continue. The frequency effect is growth as the hydration and saline concentration increases. It is implied that the single frequency measurement for evaluating the cement slurries properties may not be reliable. An implicit correlation to the interface conductivity is indicated from dispersion respond throughout hydration process.

Influence of different brine water salinity on mechanical properties of fly ash-based geopolymer cement

Purpose The purpose of this paper is to investigate the mechanical properties changing of geopolymer cement under different brine salinity. Design/methodology/approach Geopolymer Cement of Class F Fly Ash and Class G Cement slurries were prepared according to API RP 10B. The optimum alkaline activator/cement and water/cement ratio of 0.44 was used for geopolymer and Class G cement samples, respectively. The alkaline activator was prepared by mixing the proportion of Sodium Hydroxide (NaOH) solutions of 8 M and Sodium Silicate (Na2SiO3) using ratio of 1:2.5 by weight. The slurries were cured for 24 hours at 130oC and 3,000 psi in HPHT Curing Chamber followed by coring process. Both cement sample were immersed in brine water salinity up to 28 days with different brine salinity up to 30 per cent of NaCl. The mechanical properties were investigated using OYO Sonic Viewer-SX and Uniaxial Compressive Strength. The surfaces of the cement samples were extracted for Scanning Electron Microscope (SEM) and EDS tests to evaluate the morphology and chemical compositions of the cured samples. Findings The paper shows that geopolymer samples experiences strength reduction in brine water but the reduction rate of geopolymer is about half of the Ordinary Portland cement based oil well cement. The finding was also verified by SEM and EDS result. Originality/value This paper investigates the mechanical property changes of emerging geopolymer cement due to different water salinity. The results provide potential application of geopolymer cement for oil well cementing.

Formulation of geopolymer cement using mixture of slag and class f fly ash for oil well cementing

The increase in greenhouse gas emissions has been a factor for the increase in global temperature. Geopolymer cement has been intensively studied to replace conventional ordinary Portland cement, however the focus is limited to civil purposes under atmospheric conditions. This research focuses on the formulation of geopolymer cement to be used in oil well cementing application by taking account the effect of sodium hydroxide (NaoH) molarity, ratio of alkali binder and fly ash, amount of dispersant for oilwell operation under temperature ranging of 80°C and 90C° and pressure of 1000 and 3000psi. The formulated composition is tested for fluid loss where the standard has been from 60 to 80 ml. The cement slurry is cured in a 50mm x 50mm x 50mm mold for period of 24 hours. Four manipulating variables were set in formulating the cement slurry namely, the ratio between fly ash and slag to alkali binder, ratio of sodium hydroxide (NaoH) to sodium silicate, molarity of NaoH and amount of dispersant added. After running a set of 16 experiment, sample (12) was found to possess the best rheological properties and fluid loss according to API RP10B. It was found that as the curing temperature and pressure increase, the compressive strength of the formulated geopolymer cement also increased.

An alternative approach for dynamic modeling in a complexly structured and heterogeneous carbonate gas reservoir: a field case study

This paper presents an alternative approach to integrate static and dynamic data for construction of the three-dimensional (3D) dynamic reservoir model. The integrated workflow was applied to a complexly structured and heterogeneous carbonate reservoir, in Zaakher Gas Field, Southeast Asia. In this study, the number of faults which crossed along critical flow paths through fault zones were defined and modeled. Subsequently, fault zone transmissibility was calculated and modeled to be incorporated into the dynamic model. In addition, a novel methodology to determine and define the rock region model was also proposed. Construction of the dynamic model was conducted by incorporating the upscaled static geological model, fault zone transmissibility, rock region model, reservoir characteristics, and production and pressure history, as well as well completion data into the simulator. The simulation results show that the integrated workflow for 3D dynamic modeling proposed in this study has successfully improved history matching results and have a good acceptable match.