Jose C.S. Cunha

Use of Quantitative Risk Analysis for Uncertainty Quantification on Drilling Operations-Review and Lessons Learned

This paper presents comments and some background on the use of risk analysis methods in the oil and gas industry. Particularly attention is gi ven to applications developed specifically for drilling operations. A literature review emphasi zing articles written specifically for risk analysis applications on oil & gas we ll drilling operation is presented. Recommendations for procedures related to risk analysis meth ods implementation as well as an example of application and its results are presented. A Monte Carlo simulation was run to predict a cumulative distribution function for a well drilling AFE (Authorization For Expenditure.) The simulation procedure as well as the resultant function is presented.

Importance of Drilling Fluids' Rheological and Volumetric Characterization to Plan and Optimize Managed Pressure Drilling Operations

Managed Pressure Drilling (MPD) is an alternative to overbalanced and underbalanced drilling in conditions where pore pressures and fracture gradients are so close to each other (depleted reservoirs, deep and ultra-deep offshore reservoirs) that it is not possible to drill significant depths without setting a casing. While MPD enables an operator to drill longer footages without setting a casing, it requires precise estimation of equivalent circulating density (ECD) during drilling and static bottomhole pressure (SBHP) during non-drilling times. General practice in the drilling industry is to use rheological and volumetric properties of drilling fluids measured at surface to estimate ECD and SBHP. Consequently, ECD and SBHP measured using MWD and LWD tools in the field do not match the theoretical calculations. This study shows the importance of introducing the effect of downhole conditions to hydraulic equations in order to estimate ECDs and SBHPs accurately. Paraffin-based synthetic drilling fluid is used for this purpose. The effect of pressure and temperature on density of fluid is determined using PVT cell experiments. An equation relating the density of the fluid to pressure and temperature is determined using linear and non-linear regression techniques. Rheological characterization of the fluid was obtained on a Fann 75 HPHT rotational viscometer. A Bingham plastic model was used to define shear stress - shear rate relation of the fluid in all pressures and temperatures. The effect of pressure and temperature on plastic viscosity and yield point are determined using linear and non-linear regression techniques, similar to the ones used in PVT analysis. Both onshore and offshore cases are investigated and the effect of incorporating downhole effects to density and rheological parameters on ECD are analyzed.

Economic Analysis for Enhanced CO Injection and Sequestration Using Horizontal Wells

Carbon dioxide flooding has been recognized widely as one of the most effective enhanced oil recovery processes applicable for light to medium oil reservoirs. Moreover, the injection of CO 2 into an oil reservoir is a promising technology for reducing greenhouse emissions while increasing the ultimate recovery of oil. Numerical reservoir simulation is an important and inexpensive tool for designing EOR CO 2 projects and predicting optimal operational parameters. In this work, reservoir simulations performed with a compositional simulator were applied to investigate the macroscopic mechanisms of a CO 2 injection process. Horizontal injectors were used to increase injectivity. Compared to traditional vertical wells, horizontal wells are more attractive to improve CO 2 flooding economics by increasing injection rate, improving areal sweep and increasing CO 2 storage. The effects of several important parameters on the performance of the CO 2 process were studied to optimize the process. Operational parameters such as different production schemes, the injector pressure and injection rate were investigated to determine the optimal operating conditions for simultaneous objectives of higher recovery and higher CO 2 storage. The application of CO 2 flooding using horizontal wells can shorten project life, which is critical to its economics. The simulation results served as the basic input parameters for the economic analysis performed. Furthermore, net present value (NPV) and profitability index results were used to optimize the profitability of the project and to compare the CO 2 application using vertical and horizontal wells. The analysis used actual design parameters, including equipment and operating costs. The evaluation emphasized the importance of reservoir characteristics, optimum design of operation parameters and economic factors in the economic feasibility of CO 2 injection projects for enhanced oil recovery and sequestration.