Predicting Effective Permeability to Oil in Sandstone and Carbonate Reservoirs From Well-Logging Data

2011 ◽  
Vol 14 (06) ◽  
pp. 750-762 ◽  
Author(s):  
Nicolas Legrand ◽  
Joop de Kok ◽  
Pascale Neff ◽  
Torsten Clemens
Keyword(s):  
Effective Permeability ◽  
Oil And Gas ◽  
Material Balance ◽  
Total Porosity ◽  
Low Permeability ◽  
Moderate Increase ◽  
Slow Increase ◽  
Solution Gas Drive ◽  
Gas Drive ◽  
Solution Gas

Summary The fractured basement field in Yemen described in this paper is characterized by two types of fracturing: background fractures with a very low effective permeability of less than 0.001 md and fracture corridors with an effective permeability of up to several millidarcies. Except for some dissolution porosity related to fracture corridors, no significant matrix porosity is encountered (total porosity is only 1.15%). Approximately one-half of the oil in place is contained in the fracture corridors and one-half in the background fractures. Production from this field commenced in 2007. It is currently produced by depletion. Compositional grading has been observed in the 3,120-ft oil column. Despite the fact that the oil is close to bubblepoint pressure at the top of the reservoir, a moderate increase in gas/oil ratio (GOR) has been seen. Detailed studies using material balance and discrete-fracture-network (DFN) models revealed that the reason for the slow increase in GOR is the low permeability of the background fractures. The low permeability leads to viscous forces being dominant over gravity forces and, hence, limited gravity segregation of gas and oil. Because of the relatively small viscosity difference between the gas and the oil in this field(µo/µg = 6.5), the gas mobility is not much higher than the oil mobility at low gas saturations. Hence, oil and gas are produced effectively from the background fractures into the fracture corridors and the reservoir pressure is not depleting as fast as in reservoirs with higher viscosity difference between gas and oil. This results in a more effective solution-gas-drive recovery mechanism than that expected for a conventional reservoir. A number of reservoir-management strategies have been investigated. The results indicate that the low permeability of the fracture corridors and very low permeability of the background fractures lead to low recovery factors of 14% for gas injection. However, the efficiency of solution-gas drive is higher than in conventional reservoirs.

Pressure Transient Analysis of a Vertically Fractured Well Produced by Solution Gas Drive

1977 ◽  
Vol 17 (05) ◽  
pp. 369-376 ◽  
Author(s):  
R. Raghavan
Keyword(s):  
Oil And Gas ◽  
Function Concept ◽  
Pressure Function ◽  
Pressure Transient ◽  
Permeability Characteristics ◽  
Solution Gas Drive ◽  
Fluid Properties ◽  
Gas Drive ◽  
Fractured Well ◽  
Solution Gas

Abstract Pressure transient data were investigated in a homogeneous and uniform reservoir containing oil and gas and producing at a constant surface oil rate by solution gas drive by means of a vertically fractured well. The well is assumed to be located at the center of a closed-square drainage area. Gravity effects were not included. To my best knowledge, this is the first study ort the pressure transient behavior of a vertically fractured well producing by solution gas drive. producing by solution gas drive. A recent paper presented a new method for analyzing pressure data in wells producing by solution gas drive. The method incorporates changes in effective permeability and fluid properties (formation volume factor, viscosity, and gas solubility) with pressure by means of a pseudo-pressure function however, it dealt exclusively pseudo-pressure function however, it dealt exclusively with plane radial flow. This paper presents the application of that new technique to vertically fractured wells. Dimensionless groups are used throughout to extend the results to other situations having different permeabilities, spacing, reservoir thickness, porosity, etc, provided the PVT relations and relative-permeability characteristics are identical to those used in this study. The pseudo-pressure function concept used to analyze pseudo-pressure function concept used to analyze drawdown and buildup behavior extends the applicability of the results to a wide range of PVT relations and relative-permeability characteristics. Introduction In recent years, the analysis of pressure data of fractured wells has received considerable attention. However, most of this work is related to single-phase flow. An examination of the literature indicated that no rigorous study has been made regarding the pressure behavior of a vertically fractured well producing by solution gas drive. The first objective of this paper is to discuss the transient floe, behavior of the system described above. The second objective is to demonstrate the applicability of a recent technique for determining absolute formation permeability when two phases (oil and gas) are flowing simultaneously. This technique is based on using a pseudo-pressure function that rigorously incorporates changes in permeability with saturation and fluid properties permeability with saturation and fluid properties with pressure. It will be shown that, by using the procedure suggested here, better estimates of procedure suggested here, better estimates of fracture length also can be obtained. LITERATURE REVIEW General equations of motion describing multiphase flow in porous media are well known and will not be discussed here. A summary of the work in this area as if pertains to well test analysis is presented in Ref. 5. This section briefly reviews only the computation of an integral (henceforth called the pseudo-pressure function), which was used in Ref. pseudo-pressure function), which was used in Ref. 5 to analyze drawdown and buildup. In a recent paper, Fetkovich suggested that if the pseudo-pressure function, m (p), given by: (1) is used, then transient, pseudo-steady-state and steady-state multiphase flow through porous media may be described by simple expressions similar to that for the flow of a slightly compressible fluid. For example, Fetkovich suggested that for transient radial flow one can express the flow rate as (2) where to is the dimensionless time given by (3) In Eq. 2, s' represents the skin effect that, in general, includes the effects of damage in the vicinity of the wellbore, as well as a skin effect caused by the development of a gas saturation. SPEJ P. 369

scholarly journals Porous flow characteristics of solution-gas drive in tight oil reservoirs

Open Physics ◽  
2018 ◽  
Vol 16 (1) ◽  
pp. 412-418
Author(s):  
Xiao Qianhua ◽  
Wang Zhiyuan ◽  
Yang Zhengming ◽  
Liu Xuewei ◽  
Wei Yunyun
Keyword(s):  
Flow Resistance ◽  
Material Balance ◽  
Oil Reservoirs ◽  
Tight Oil ◽  
Porous Flow ◽  
Drainage Radius ◽  
Solution Gas Drive ◽  
Tight Oil Reservoirs ◽  
Gas Drive ◽  
Solution Gas

Abstract The variation of porous flow resistance of solution-gas drive for tight oil reservoirs has been studied by designing new experimental equipment. The results show that the relation between the porous flow resistance gradient and pressure is the exponential function. The solution-gas driving resistance is determined by a combination of factors, such as the gas-oil ratio, density, viscosity, permeability, porosity and the Jamin effect. Based on the material balance and the flow resistance gradient equation, a new governing equation for solution-gas drive is established. After coupling with the nonlinear equation of elastic drive, the drainage radius of solution-gas drive is found to be very small and decreases rapidly when the bottom-hole pressure approaches the bubble-point value. Pressure distribution of the solution-gas drive is non-linear, and the values decrease sharply as it approaches the well bore. The productivity is rather low despite being strongly influenced by permeability. Therefore, stimulated reservoir volume (SRV) is the essential measure taken for effective development for tight oil reservoirs.

A Study of Heavy Oil Solution Gas Drive for Hamaca Field: Depletion Studies and Interpretations

2004 ◽  
Author(s):  
Cengiz Satik ◽  
Carlon Robertson ◽  
Bayram Kalpakci ◽  
Deepak Gupta
Keyword(s):  
Heavy Oil ◽  
Solution Gas Drive ◽  
Gas Drive ◽  
Solution Gas
Sign in / Sign up

Export Citation Format

Share Document