جستجوی مقالات مرتبط با کلیدواژه « FRACTURED RESERVOIR » در نشریات گروه « فنی و مهندسی »

The influence of fracture network on quality of reservoir, emphasize the importance of study of fractured reservoirs. The characterization of fractured reservoirs is complex. We are going to study fractures of one of the oil fields of Persian Gulf by discrete fracture network modeling. Fracture modeling is often based on very limited well data and therefore is subject to high uncertainty. Typically, the standard modeling workflow uses interpolation algorithms to predict the fracture spatial distribution. This paper shows an alternative workflow for improving fracture modeling between wells through the use of seismic attributes. The main objective of this paper is to compare fracture intensity models guided by the two approaches: The standard interpolation based approach, and the seismic based approach using attributes sensitive to faults. The difference between these two methods lies in the way fracture intensity is modeled. Fracture intensity is an important fracture attribute because it guides the fracture simulation. It is estimated from the fracture point data derived from the well data and upscaled into the model. Typically, the standard method employs Kriging or Sequential Gaussian Simulation (SGS) to interpolate the fracture intensity of the 3D grid. This method can deliver highly inaccurate results in case of limited well control. The second approach tries to reduce this uncertainty, through controlling the fracture intensity interpolation via seismic attributes. Seismic attributes can be used as secondary input for the interpolation of the fracture. The preferred interpolation algorithm is collocated co-Kriging because one has full control over the radius of influence of the well data. In addition the influence of the secondary input, the seismic attribute, is controlled via its correlation factor with the well data. A comparison of these two methods provides insight into the complexity and uncertainty involved in fracture modeling.

The gravitational drainage of oil in gas-invaded zone is identified as the major production mechanism in carbonate reservoirs. Oil is kept in a matrix block surrounded by gas and then subject to two distinct and opposing forces. Due to the difference between oil and gas densities, gravitational forces tend to expel oil through the lower part of the block, while oil-rock adhesive force acts to peneterate within the rock. Drainage arises when “gravitational” and “capillary” forces coincide. In this study, the mathematical modelling of gravitational drainage in naturally fractured reservoir is presented which involve capillary, gravitational, and infiltration processes. A simple approach was proposed to simulate gas-oil gravity drainage process in fractured porous media using an appropriate fracture capillary pressure. The permeability value is approximated by the location of fracture in the stack block. The capillary pressure in horizontal fracture is related to height of fracture in stack block to gas-oil interface. Numerical simulation results revealed good agreement with experimental data. This study revealed that capillary continuity and fracture transmissibility are the most important factors in oil recovery by gravitational drinage mechanism.

The main part of oil produced in Middle East is supplied from carbonate reservoirs, the majority of which are fractured ones. These reservoirs produce higher rates at their early ages which is followed by lower rates   afterwards, leading to low overall recovery values. The purpose of most drillings is to increase production over longer periods. A reservoir simulation study was carried out on a fractured Middle Eastern carbonate field to determine the optimal production strategy. The three possible methods - natural depletion, gas injection and water injection- were then compared. Results indicated that water injection exhibits better recovery values than gas injection and natural depletion. This is expected since rock exhibits intermediate oil-wetting values, meaning that higher recoveries are achieved due to water flooding. The presence of fractured rocks led to early breakthrough and lower recoveries in gas injection method. The different physical mechanisms affecting oil recovery values are discussed and a few suggestion were presented for other fields possessing the same fracture properties and wet-abilities.