Deep gas reservoirs are going to play more important roles in meeting growing demand of natural gas throughout the world. Due to extreme conditions of downhole stresses, pressure and temperature that occur in deep gas wells, maintaining cement mechanical integrity and zonal isolation have become critical concerns of industry during drilling, completion, and production of such wells. Cement sheath is expected to provide a flawless annular seal between casing and formation along the wellbore. However; cement failure cases which are being reported regularly show that there is still need for understanding extreme downhole conditions and the behavior of cement sheath experiencing such an environment. Although Uniaxial Compressive Strength (UCS) of cement is commonly regarded as the most important mechanical property of cement, recent theoretical and experimental results show that other mechanical properties of cement can be even more determinative in its failure.In this study, Finite Element Method (FEM), a widely-used robust numerical tool, is used for simulation of the downhole environment by modeling temperature, pressures, stresses, downhole materials and their interactions. Using this approach magnitude, direction and type of induced stresses in casing, cement, and formation have been determined. Furthermore; a series of sensitivity analyses was performed to reveal the effects of variation of various parameters such as casing internal pressure, differential horizontal stress and casing eccentricity, on the induced stresses in the cement sheath.Radial, tangential and von Mises stress profiles in the deep gas wells cements were investigated. Furthermore, the effect of casing internal pressure, differential horizontal stress and casing eccentricity were studied in the model. Results show that deep gas wells' cements experience extreme amounts of thermal and mechanical stresses and special consideration is required in cement selection.

Several parameters are involved in a hydraulic-fracturingoperation, which is a technique used mainly in tight formations to enhance productivity. Formation properties, state of stresses in the field, injecting fluid characteristics, and pumping rate are among several parameters that can influence the process. Numerical analysis is conventionally run to simulate the hydraulic-fracturing process. Before operating the expensive fracturing job in the field, however, it would be useful to understand the effect of various parameters by conducting physical experiments in the lab. Laboratory experiments are also valuable for validating the numerical simulations. Applying the scaling laws, which are to correspond to the field operation with the test performed in the lab, are necessary to draw valid conclusions from the experiments. Dimensionless parameters are introduced through the scaling laws that are used to scale-down different parameters including the hole size, pump rate and fluid viscosity to that of the lab scale. Sample preparation and following a consistent and correct test procedure in the lab, however, are two other important factors that play a substantial role in obtaining valid results. The focus of this peer-reviewed paper is to address the latter aspect; however, a review of different scaling laws proposed and used will be given.The results presented in this study are the lab tests conducted using a true triaxial stress cell (TTSC), which allows simulation of hydraulic-fracturing under true field stress conditions where three independent stresses are applied to a cubic rock sample.

Optimization of costly drilling operations is essential to reduce the overall costs of oil and gas extraction. Simulation of these operations can yield a better selection of parameters for maximum drilling efficiency. One of the most cost efficient methods to do so is by computer modeling. Because of the complex nature of the cutting process, no analytical methods can be used for its modeling and the numerical methods are the only option. FEM and Discrete Element Method (DEM) are the most commonly used numerical methods for this purpose. One of the best features of the DEM is that it is very suitable for discontinuous environment and no special treatment or process is required in tracking the produced cracks and fragmentation. Also depending on the depth of cut, it can both simulate ductile or brittle failures. In current study, a 2D computer model was developed using the particle flow code (PFC2D) to simulate the cutting action of a single cutter. PFC uses the DEM to model a rock sample by fine cylinders or disks. The properties of the Berea sandstone were considered in our modeling. A good match of mechanical properties was obtained for the rock model by adjusting micro parameters of the contacts between the constituting balls and the results of the simulation are compared to laboratory data.

Populating water saturation is a critical step in dynamic modelling. This work introduces a different height function that equates directly with the Leverett-J formula. In doing so, the model initialises under quiescent conditions without the need for end-point scaling. The resulting water saturation is a function of permeability, porosity, clay volume and height above the free water level. The Vcl—or clay content—is an important feature in this formulation because it compensates between extreme values of permeability and porosity. This peer-reviewed paper describes how a single height function was sufficient to match the log-derived water saturation for all wells in the Coracle sand of the Surprise Field in the North Sea. The process involved fitting a simple height formula, with the least possible parameters, to the J-function calculated from all the special core analysis (SCAL) data. These parameters were then tuned to match the log-derived water saturation. This technique was subsequently used in other fields where a single height function, which honoured the measured capillary pressures, accurately matched water saturation in all of the wells.

A new simulator that has been designed and built at Curtin University can simulate rock drilling in different environments. Horizontal and vertical stresses, pore pressure, circulation pressure, rate of penetration, depth of cut, and torque can be precisely monitored by the simulator to investigate the effects of each of the parameters for optimisation purposes. A computer simulation is also initiated using Particle Flow Code in two dimensions (PFC2D) for further studies on rock cutting mechanism and direct numerical results. The results obtained by combining these two methods are of high reliability for predicting cutting behaviour of different bits. This paper presents the new drilling equipment and the results of studies on sandstone drilling. Previously, the single cutter scratching test on Mountain Gold sandstone was modelled by PFC2D and the results were very similar to the experimental results. Here, custom-made full-face PDC bits are used for drilling in cubical samples of synthetic sandstones with known properties. Water is used as the drilling fluid and the rock sample is drilled under atmospheric conditions. Bit torque, WOB and ROP are monitored to obtain optimum drilling response in terms of ROP and specific energy. The obtained results are of high importance in predicting drilling speed and optimum drilling parameters. This can improve well planning and has the potential to reduce the cost of drilling wells.