Gas reservoirs are known to be difficult to mine due to low permeability. Several studies have been conducted on fracturing stimulation so that the productivity of this tight gas reservoir can be increased. For this reason, this project will focus on frac stimulation for low-density gas with a focus on proppant diameter.
Thus, the objective of this project was to determine and analyze the value of dimensionless fracture conductivity that can result in a high value of fracture half-length, which will be used for simulation with 4 different sizes of proppant (median diameter) and its permeability on the production responses. In the early phase of this project, tight gas reservoir and fracture stimulation research will be conducted. In conclusion, the productivity of the tight gas reservoir can be increased by performing fracture stimulation on the reservoir, and it depends on several fracture parameters, such as the dimensionless fracture conductivity, fracture half-length, fracture width, proppant permeability, proppant median diameter and etc.
I am grateful to Allah, my Lord and Cherisher, for guiding me to conceptualize, develop and complete my final year project, Fracture Stimulation for Tight Gas Reservoir. Thanks to my parents and family for understanding the amount of time I need to complete this project.
Introduction
- Background Study
- Significant of the project
- Objective
- Scope of Study
- The Relevancy of the Project
- FeasibilityoftheProject
After acquiring the FCD, we will use it to evaluate the median diameter of the proppant, which will allow obtaining a high value of the proppant permeability, which will ultimately increase the productivity in terms of the AOF of the reservoir. Through this project, data such as the absolute open flow (AOF) of the well will be generated using analytical solutions. This project will be carried out mainly by researching the topic and collecting the necessary data.
From the data collected, calculations will be made using appropriate formulas such as the calculation of the dimensionless fractional conductance and etc. Some experts also believe that gas consumption may exceed that of oil by the year 2025. As a result, future energy sources of the world, especially gas will be found in what we consider today as unconventional reservoirs, especially low-permeability reservoirs in shale, siltstones, fine-grained sands and carbonates.
Because of this, this project is important so that those unconventional gases, namely in tight gas reservoir, can be produced optimally and economically to fill all those gaps. This project is primarily based on research and stimulation using software that is available at UTP itself such as WellFlo.
Theory and Literature Review
Tight Gas Reservoir
The blue areas are pore space and would contain natural gas in a producing gas field. Tight gas reservoirs are often considered to incur higher costs and risks than conventional reservoirs. Geologists note that techniques such as regional facies mapping and sequence stratigraphy, which are useful for finding and delineating conventional reservoirs, are often ineffective for tight reservoirs.
Fracture Stimulation
To optimize the hydraulic fracture design, a 1-D geoecbanic survey was requested to estimate the hydraulic fracture toughness of the rock. A 1-D Mechanical Earth Model (MEM) was constructed and the fault breakdown pressure was estimated as a result of the model. Advanced sonic processing performed before and after fracturing, providing estimated pre- and post-hydraulic minimum and maximum horizontal stress.
Hydraulic fracturing design and procedure were then developed based on the results of the model. The pad (pure fluid) is first pumped to create the fractures and to establish propagation - the fracture grows both up and down and out. The proppant-laden slurry is then pumped - this slurry continues to expand the fractures and simultaneously carries and places the proppants deep within.
The carrier fluid chemically breaks down to a lower viscosity and flows back out of the well. Highly conductive, propped fractures that allow oil and/or gas to flow easily from the ends of the formation into the well.
Formula's and Calculation
However, determining when a tight gas well has defined its drainage area can be quite challenging. Theory says that the time to pseudo-steady state can be estimated from the equation below;. The straight line portion of the Hornet plot can be extrapolated to a false reservoir pressure referred to as P*.
However, to obtain a meaningful estimate of P* from the pressure transient analysis, the well must be closed long enough to achieve pseudo-radial flow. The resulting estimate of P* must be corrected to an average reservoir pressure before it can be used for material balance calculations. The cut-in time required to achieve pseudo-radial flow can be estimated using the equation below for a hydraulically fractured well.
If proppant-induced pressure responses negatively affect the distribution of proppant in a fracture, then they definitely have a negative effect on the production responseYl. The pressure response without proppant is representative of what would happen if proppant-induced friction did not occur. Because there is no proppant-induced pressure effect, this would imply that if proppant were present, it is easy to penetrate and distribute in the fracture.
In our study we asked whether the production response was influenced by the nature of the pressure response induced by the proppant. The proppant enters the fracture, the pressure flexes, and the proppant continues to bridge the fracture. The rapid pressure drop after tripping shows that the proppant bridged asymmetrically within the fracture.
Intuitively, the support distribution with this response would be expected to be better than the response observed in Figure 2.7. However, the fracture image dll,ta shows the increase in rupture height with little increase in pressure caused by the support. If small pressure deflections caused by the support adversely affect the lateral distribution of the propellant, figure 2.8 may not be the desired response either.
Methodology
Project Activities
Gantt Chart and Key Milestone
Material, Software and Equipment
Result and Discussion
Result and Discussion
From the spreadsheet, at a pressure of 4500 psia (reservoir pressure) we get the WGR to be 0.871 STB/MMSCF. From the IPR cure we can obtain the AOF for the reservoir which is 50,299 MMscf/d. This AOF indicates the AOF of the reservoir before fracture is introduced into the production interval.
From Figures 4.13 to 4.14 and Table 4.9, we can see that as we decrease the dimensionless fracture conductance, half the fracture length will increase for each permeability. Thus, we chose FCD = l to use in our fracture simulation using WellFlo as it will generate the highest fracture half-length. Proppant permeability will increase as the median diameter of the proppant material increases and the highest proppant permeability is when we use proppant with an average diameter of 0.691 mm, which gives the nse proppant permeability of 340 md.
Because of that, we chose proppant with a median diameter of 0.691 mm to be nsed for fracture jobs.
Conclusion and Recommendation
Conclusion
Recommendation
Kanitthom Adisosupawat, Chee Phuat Tan, Leo Anis, Aurifullah Vantala, Reayad Juman, Barry Boyce, APICO (Thailand); 2011; Enhanced geomechanical modeling with advanced sonic processing to delineate and evaluate a tight gas reservoir.
