Objective<br />To compare the Performance of Horizontal and Vertical Hydraulically Fractured Wells in a Tight Gas Reservoir<br />04<br />
Scope<br /><ul><li>In years to come, when conventional resources of Oil and Gas will be depleted, the world will have to look towards Unconventional Resources among which Tight Gas Reservoirs are one of the options.
The question arises “Which is the suitable method to develop a particular Tight Gas Reservoir?”
Our project can serve as a prototype which can be scaled up for the real data.</li></ul>05<br />
TIGHT GAS RESERVOIRS<br />A Brief Introduction<br />AsifAzhar (PE-033)<br />
Introduction to Tight Gas Reservoirs<br />Tight gas is the term commonly used to refer low permeability reservoirs that produce mainly dry natural gas.<br />‘Tight Gas Sands’ by Stephen A. Holditch, SPE Texas A &M U<br />07<br />
Definition of Tight Gas Reservoir<br />“ . . . The best definition of tight gas reservoir is a reservoir that cannot be produced at economic flow rates nor recover economic volumes of natural gas unless the well is stimulated by a large hydraulic fracture treatment or produced by the use of a horizontal wellbore or multilateral wellbores . . . ”<br />‘Tight Gas Sands’ by Stephen A. Holditch, SPE Texas A &M U<br />08<br />
What Makes a Reservoir Tight?<br /><ul><li> The original depositional fabric itself was tight.
The original sedimentary fabric have been subsequently reduced in porosity by post depositional diagenesis to unacceptably low amounts.</li></ul>‘What is considered a Tight Gas Reservoir’ by Ravi Mishra<br />09<br />
Possible Candidates for TGR in Pakistan<br /><ul><li> Lower Goru Tight Sands
Reservoir Simulation<br /><ul><li> Reservoir simulation is an area of reservoir engineering in which computer models are used to predict the flow of fluids (typically, oil, water, and gas) through porous media.
Gordon Adamson in his article “Simulation Throughout the Life of a Reservoir” writes:</li></ul>“Simulation is one of the most powerful tools for guiding reservoir management decisions. From planning early production wells and designing surface facilities to diagnosing problems with enhanced recovery techniques, reservoir simulator allow engineers to predict and visualize fluid flow more efficiently than ever before.”<br />www.wikipedia.org <br />16<br />
Simulation Approaches<br /><ul><li>Single Well Simulation
Flow Geometries and Dimensions (contd.)<br />One-Dimensional Flow <br /><ul><li> Well test analysis
Flow is constrained to the r-direction </li></ul>Two-Dimensional Flow<br /><ul><li> Single well problems where gravity and/ or layering effects are significant. </li></ul>Three-Dimensional Flow<br /><ul><li> Property variation in all three directions.</li></ul>z<br />z<br />r<br />r<br />θ<br />Radial or Cylindrical Geometry<br />21<br />
Cases for Comparison<br />Vertical Well<br />Vertical Well<br />Fracture Height<br />Fracture Height<br />Horizontal Well<br />Horizontal Well<br />When the fracture penetrates half of the vertical well length<br />When the fracture penetrates the total vertical well length<br />CASE: 01<br />CASE: 02<br />Vertical Well<br />Fracture Height<br />Horizontal Well<br />When the fracture penetrates quarter of the vertical well length<br />CASE: 03<br />47<br />
The decline in the production rate is faster due to the closed reservoir system,
The cumulative production is more or less same,
Economics will dictate the optimum length of the horizontal well or the fracture half length,
In case of fractured wells same results can be achieved by either increasing the half length or the height of the fracture.
Since the area open to flow for the fractured well is more than that of the horizontal well, its productivity index is also greater. However achieving fracture half lengths similar to the length of the horizontal wells is impossible in practice.
The productivity index increases almost linearly for the horizontal well.
For vertical fractured wells the increase in productivity index becomes less as the length of the fracture increases.
It will therefore be a matter of economics to decide between the fractured wells and the horizontal well.</li></ul>58<br />