Effects of Fracture Geometry On Well Productivity

PETE 3715Tuesday 4/22/2014

Group Members: •Alan Alexeyev•Ahmed Mohamed•Aziz Al-Umairy•Pradyumn Singh

Components of Fracture Geometry and determining factors.

• Parameters:•Half Length (Xf )•Fracture Width (w)•Fracture Height (hf)•Fracture Conductivity ( CfD)•Proppant Number (Np)

Introduction • The hydraulic fracture design is highly dependent on

reservoir permeability

• What fracturing accomplishes is to alter the way fluids enter the wellbore . It changes the flow from near well radial flow to linear or bilinear flow.

• Optimal levels of fracture dimensions are needed for maximizing the productivity index which Proppant Number and conductivity.

•Generally for higher permeability reservoirs , a large Fracture width is necessary for optimal production. Height and length are of secondary importance.

•For lower permeability reservoirs , fracture permeability , width and height are of secondary importance. Length of the fracture is given more importance.

PKN & GDK Models

There are two models which help us to determine the fracture Geometry :

PKN : This option is most applicable for fractures with length to height aspect ratios less than unity or for fractures which display slip at the upper and lower boundaries. λ= 2L/H < 1 Figure 1. PKN model.

GDK : This option is most applicable for fractures with length to height aspect ratios less than unity or for fractures which display slip at the upper and lower boundaries. λ= 2L/H < 1

• Figure 2.GDK Model.

Length and Conductivity of Fractures

•Every hydraulic Fracture can be characterized by its length, conductivity and skin effect. However , we are going to take skin effect as zero throughout the presentation.

Relative capacity , a = k= permeability half length kf = fracture permeability w= fracture width

•Relative Capacity is important because smaller values of relative capacity implies large fracture permeability-width product and thus a high conductivity fracture.

•Conductivity •

Figure 17.4

Fracture Width •It is the horizontal length of the propped fracture.

•Formula

Figure 17.4

Figure 17.9

Figure 17.8

How Fracture Geometry Effects Production

Productivity Index •Until the optimal level of width and half length ,

Productivity index keeps increasing. Optimal level of conductivity is 1.6 .

Example: Calculation of the optimal fracture dimensions and maximum pss Productivity Index in the oil well.

Given Data: k = 15 mdBo= 1.1 rsb/stbμ= 1 cpMass of proppant (Mp) = 150,000 lbProppant specific gravity = 2.65Φ(Porosity) = 0.38Kf = 60000mdh(reservoir) = 50ft h(fracture) = 100ftArea = 4*106 sq.ft.

Find optimal dimensions, pseudosteady-state productivity index and folds of increase from fracturing.

Example: Calculation of Fracture Width and Length with a Newtonian Fluid using PKN Model

Find maximum and average fracture widths when fracture half length is 500 ft. μapparent=100cp, injection rate qi=40bpm. Poisson ratio v= 0.25E=4*10^6hf=100ftxf=1000ft