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Abstract Pore pressure is a key parameter in controlling the well in terms of reservoir fluid pressure. An accurate estimation of pore pressure yields to better mud weight proposition and pressure balance in the bore hole. Current well known methods of pore pressure prediction are mainly based on the differences between the recorded amount and normal trend in sonic wave velocity, formation resistivity factor (FRF), or d-exponent (a function of drilling parameters) in overpressured zone. The majority of the techniques are based on the compaction of specific formation type which need localization or calibration. They occasionally fail to proper response in carbonate reservoirs. In this research, a new method for calculating the pore pressure has been obtained using the compressibility attribute of reservoir rock. In the case of overpressure generation by undercompaction (which is the case in most of the reservoirs), pore pressure is depended on the changes in pore space which is a function of rock and pore compressibility. In a simple way, pore space decreases while the formation undergoes compaction and this imposes pressure on the fluid which fills the pores. Generally, rock compressibility has minor changes over a specific formation, but even this small amount must be considered. Thus, the statistical tools should be used to distribute the compressibility over the formation. Therefore, based on the bulk and pore compressibility achieved from the special core analysis (SCAL) or well logs in one well, the pore pressure in the other locations of a formation could be predicted.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.31)
- North America > United States > Wyoming > Wind River Basin > Madison Formation (0.99)
- North America > United States > South Dakota > Williston Basin (0.99)
- North America > United States > North Dakota > Williston Basin (0.99)
- North America > United States > Montana > Williston Basin (0.99)
ABSTRACT: The work presented in this paper investigate developing a mathematical formulation using finite-difference techniques to solve the geomechanics equations consistent with the mathematical formulation for solving fluid flow equations. The key considerations are consistency of the mathematical formulation (finite-difference technique) for both geomechanics and fluid flow calculations, and ease of implementing this formulation. Results show that it successfully model the induce stress changes (?s) in the reservoir rock created by either fluid production or injection. Also, the results obtained from applying finite-difference technique in solving the geomechanics equations are comparable to that obtained from using finite-element techniques. The experience obtained from this work indicates that fluid withdrawal or injection can have a great impact reservoir stresses. The provided solution can be used as a preliminary geomechanics and fluid flow modeling tool to assess impact of fluid movement on reservoir stresses. A more advanced modeling workflow/software package can be sought if required. 1. INTRODUCTION Fluids withdrawal from stress sensitive reservoirs or incompetent formations can cause rock deformation. Although in some petroleum reservoir rock compaction has been identified as a driving mechanism of oil and gas production, its side effects, such as surface or seabed subsidence, are highly undesirable. Surface facilities and subsurface tubulars could be damaged [1]. Several significant changes take place when we alter hydrocarbon reservoirs. These changes include reservoir fluid pressure, reservoir temperature, phase saturations, and local rock stresses in the reservoir and the surrounding rock. However, for more accurate fluid flow and rock mechanics modeling a coupled geomechanics and fluid flow sub-surface simulator should be used. Rock compaction can cause land subsidence, well-tubular collapse, surface facility damage, reservoir permeability alteration, fracture inducement and fault alterations. It is important to know if the existing faults will be affected by fluid production or injection.
Abstract Knowledge of pore fluid pressure is essential for safe drilling and efficient reservoir modelling. An accurate estimation of pore pressure allows for more efficient selection of casing points and a reliable mud weight design. Current commonly used methods of pore pressure prediction are based on the difference between a ‘normal trend’ in sonic wave velocity, formation resistivity factor (FRF), or d-exponent (a function of drilling parameters) and the observed value of these parameters in over-pressured zones. The majority of the techniques are based on shale behaviour, which typically exhibits a strong relationship between porosity and pore fluid pressure. However, carbonate rocks are stiffer and may contain over-pressures without any associated influence on porosity. Indeed, the application of common pore pressure prediction methods to carbonate rocks can yield large and potentially dangerous errors, even suggesting absences or decrease in abnormal pressure in zones of high magnitude over-pressure. In some cases, the hypothesises which been in the conventional methods seems to be flawed in some cases where pore pressure decreases by depth. In this research, a new method for effective stress calculation has been obtained using the compressibility attribute of reservoir rocks. In the case of over-pressure generation by undercompaction (as occurs in most clastic over-pressured sequences), pore pressure is dependent on the changes in pore space, which is a function of rock and pore compressibility. In simple terms, pore space decreases while the formation under goes compaction, and this imposes pressure on the fluid which fills the pores. Carbonate reservoirs in two fields in Iran have been investigated to establish pore fluid pressure generation mechanisms, and to attempt new methods for pore pressure prediction in carbonate rocks.
- North America > United States (1.00)
- North America > Canada (1.00)
- Asia > Middle East > Iran > Khuzestan (0.28)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Economic Geology > Petroleum Geology (1.00)
- (2 more...)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > Wyoming > Wind River Basin > Madison Formation (0.99)
- North America > United States > South Dakota > Williston Basin (0.99)
- North America > United States > North Dakota > Williston Basin (0.99)
- (17 more...)