An application of integration of reservoir production data in analysis for nature of fault is presented in this paper. The real data of a Gas Field (namely RS Gas Field) of L-Basin of Pakistan are used. The basic concept behind this work is to enlighten the importance of production data analysis in a broader way like for finding out the nature of fault i.e. conductive or non-conductive and if it is conductive, what is the leakage factor of the fault etc. Normally in the case of fault analysis we rely on geological and geophysical methods to some extent but in some cases where these geological and geophysical methods are not able to reach any final and firm conclusion because of data limitation or any other reason, production data analysis may play a great role in answering the ambiguities regarding any fault/faults present there. This paper describes the successful implementation of reservoir production data analysis in RS Gas Field where the main uncertainties were identified during initial stage of field development when location of new development well was going to be marked. Numbers and locations of well are important factors of Oil and Gas Filed Developments; but specifically, for Gas Field Development, these factors become more crucial as compared to Oil Field Development; so clear knowledge of any heterogeneity, barrier, boundary or fault is necessary to develop a gas field optimally and economically.
The RS concession lies in the L-Basin of Pakistan and in a highly prospective area where the large gas fields of Pakistan are found. The primary objective in this area is the M-Limestone; the secondary objective was the U-Limestone. Both are of early Eocene age. The Late Cretaceous Sandstone provided a tertiary objective. The source rock for the gas is the Lower Cretaceous Shales. Seal for the M-Limestone is provided by the S-Shale, for the U-Limestone, seal is provided by the G-shale.
RS gas field was brought on production in April 2010 with an initial production rate of 16.5 MMscfd gas. Presently (December 2015), the well is producing 14 MMscfd gas, thus showing a decline of 3.24% per year.
After production of more than five years of RS-1 well, the reservoir has been appraised and level of confidence has been increased on initial gas in place estimated through different methods. For further field development, the development well (RS-2) was proposed on the south of the RS-1 (
1) The fault near the RS-1 Well is a sealing fault
2) East and West compartment of the reservoir along the fault are not in communication
3) West part may be different reservoir or may not be any reservoir because of lack of seismic data control on that side
The location for RS-2 well was proposed on the basis of some relatively high tops of reservoir. Top of reservoir in RS-1 Well is 1290 m whereas in proposed RS-2 well top of reservoir is 1285 m. It indicates additional 5 m of reservoir in proposed RS-2 well.
To determine the nature of fault of RS Gas Field Structure, study will be carried
out in two stages. In first stage the pressure and production history will be used in order to calculate initial gas in place of RS Gas Reservoir. This initial gas in place will be verified by volumetric estimation method. If initial gas in place from both the methods is in agreement it will show that dynamic and static methods are on same page that is fault is non-sealing. If it will be the case then further investigation regarding the degree of leakage of fault will be carried out through simulation as shown in
This section is concerned with fluid flow in the bulk of the RS Gas Reservoir. The integration of geology and well test analyses will be very helpful [
1) Planning reservoir development strategies.
2) Optimizing off take rates at field and reservoir layer level.
3) Marking initial well locations.
4) Designing initial well completions and identifying subsequent interventions.
Knowledge of reservoir drive mechanism is necessary in order to prepare dynamic model to calculate initial gas in-place [
To investigate the drive mechanism of RS Gas Reservoir the P/Z Vs Gp Plot (
Year | Pressure (P*)/psi | Z | Gp/BSCF | P/Z |
---|---|---|---|---|
Initial | 2080 | 0.9732 | 0 | 2137 |
2011 | 1967.7 | 0.9725 | 7.2517 | 2023 |
2012 | 1911 | 0.9723 | 12.713 | 1965 |
2013 | 1866 | 0.9721 | 19.242 | 1920 |
2015 | 1789 | 0.9720 | 27.917 | 1841 |
For a volumetric reservoir, the relationship between (P/Z) and Gp is essentially linear because of volumetric depletion of gas reservoir and by extrapolation of the straight line to abscissa, i.e., at P/Z = 0, gives the value of the gas initially in place as G = Gp [
After confirming by P/Z Vs Gp plot that there is water encroachment in the reservoir [
Cole plot of RS Gas Reservoir (
Material Balance Method is adopted to estimate the initial gas in place of Jin Gas Reservoir by using the pressure values obtained by well test interpretation using the commercial software. The material balance is based on the principle of the conservation of mass:
Mass of fluids originally in place = Fluids produced + Remaining fluids in place.
The material balance program uses a conceptual model of the reservoir to predict the reservoir behavior based on the effects of reservoir fluids production [
Havlena-Odeh graphical method was adopted to perform material balance calculations which matched with Hurst-Everdingen Dake Radial Aquifer model [
Reservoir Driver Mechanism indices are also calculated and plotted (
Material balance estimates are also validated by history matching of production and pressures which showed good match (
The accurate and perfect history matching is achieved through simulation which indicates the authenticity and validity of results of different parameters of reservoir as well as aquifer [
The Initial Gas In-Place of RS Gas Field calculated by Material Balance is also verified by Volumetric Reserve Estimation Method. Volumetric Method uses
Year | Pressure/ psi | Z | Gp/BSCF | P/Z | We/ MMRB | Gp-(We/Bg) /BSCF |
---|---|---|---|---|---|---|
Initial | 2080 | 0.9732 | 0 | 2137 | 0 | 0.000 |
2011 | 1968 | 0.9725 | 7.2517 | 2023 | 3.168 | 5.280 |
2012 | 1911 | 0.9723 | 12.713 | 1965 | 7.637 | 8.044 |
2013 | 1866 | 0.9721 | 19.242 | 1920 | 13.935 | 10.607 |
2015 | 1789 | 0.9720 | 27.917 | 1841 | 23.086 | 13.176 |
static properties of the reservoir and Material Balance Method is the dynamic model of the reservoir [
Firstly the reservoir is considered as rectangular in shape (
where G means gas in place (SCF), A is reservoir area (acres), h shows reservoir thickness (feet), θ indicates porosity (fractions), Swi is water saturation (fractions) and Bgi is gas formation volume factor (ft3/SCF). NTG in the
By using Equation (1)