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Simulating Pore Pressure driven fractures in rock sample under well-bore conditions

IP.com Disclosure Number: IPCOM000245993D
Publication Date: 2016-Apr-22
Document File: 4 page(s) / 452K

Publishing Venue

The IP.com Prior Art Database

Abstract

Hydraulic Fracturing (HF) is used to enhance production rate in oil/gas wells where formations exhibit low permeability. Successful HF operation depends on designing a treatment that targets a specific formation such that fracture height is restrained within the formation but high fracture depths are attained. Actual Fracture height and depth depend on many factors such as (i) Closure Stress Differences, (ii) Formation Thickness Effects, (iii) Fracture "Pressure", (iv) Modulus Contrasts Bedding Plane Slip, (v) Rock Ductility, (vi) Stress/Fluid Pressure Gradients Strength Differences, and (vii) Presence of Natural Fractures.

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Simulating Pore Pressure driven fractures in rock sample under well-bore conditions.

Summary


Hydraulic Fracturing (HF) is used to enhance production rate in oil/gas wells where formations exhibit low permeability. Successful HF operation depends on designing a treatment that targets a specific formation such that fracture height is restrained within the formation but high fracture depths are attained. Actual Fracture height and depth depend on many factors such as (i) Closure Stress Differences, (ii) Formation Thickness Effects, (iii) Fracture “Pressure”, (iv) Modulus Contrasts Bedding Plane Slip, (v) Rock Ductility, (vi) Stress/Fluid Pressure Gradients Strength Differences, and (vii) Presence of Natural Fractures. Figure 1. shows a case where perforated formation if fractured incorrectly deviates from original intent thus damaging an aquifer.

 
 

Figure 1

 
 


In order to optimize the HF design an assessment of porous rocks’ fracture mechanics at downhole condition is crucial for design engineers who can then use experimental data to validate and correct numerical simulation algorithms prior to implementation stage. This paper describes a Laboratory setup whereby such experimental data can be gathered.

Description of Laboratory Apparatus

An experimental setup for simulating pore pressure driven fractures under High Pressure, High Temperature conditions is depicted in Figure 2. A cylindrical pressure Vessel with embedded or external heating device becomes the test chamber which provides the confining pressure and downhole temperature conditions by means of digital control of the said parameters through an external Computer. A sample of formation that is to be evaluated is machined to have a through hole. This forms an un-notched sample and if a notched sample is desired a two-wing crack can be machined as depicted in figure 2(a). The desired sample is then assembled by putting a silicon rubber sleeve and having cover plates with O-rings seal off the pressure vessel as shown in Figure 2(b). The silicon Rubber sleeve has series of strain gauges installed on it outer surface and allows for measurement of radial and tangential displacement of the rubber sleeve. The silicon rubber sleeve also serves to isolate the formation sample from surrounding fluid, such as water or oil that is used to apply confining pressure.

Once the Test Chamber is assembled, high pressure and temperatures under control of computer are applied to reach desired test conditions. The baseline stresses exhibited by the strain gauges on the silicon sleeve are measured and normalized after reaching steady state. At this time, the desired fracturing fluid is injected via a pulseless hydraulic pump into the central hole of the formation sample. Two modes of experiment are possible either by using Constant pressure rate or a constant injection rate of fracturing fluid. By measuring the change the tangential and radial displacement, the effect of fracturing fluid can be evaluated. By...