Non-Darcy Flow in Wells With Finite-Conductivity Vertical Fractures

Abstract

Several methods have been proposed in the literature for analyzing drawdown data for the determination of fracture conductivity of vertically fractured wells. These techniques have paved accurate, but in some cases the fracture conductivity calculated is much smaller than anticipated. This study shows that producing fractured wells at high flow rates will cause nondarcy effects in the fracture, resulting in a pessimistic fracture conductivity.Numerical and semianalytical models were developed to analyze the unsteady flow behavior of finite conductivity fractures producing at high flow rates. Two methods are presented for determining the true fracture conductivity when drawdown data are available at two different flow rates. The amount of turbulent effects also is quantified by the techniques. Examples are presented to illustrate the solution methods. Introduction The increasing use of hydraulic fracturing as a means of improving the productivity of oil and gas wells in low-permeability formations has resulted in many research efforts aimed at increasing fracturing capabilities as well as evaluating the characteristics of the fracture in the postfracturing period. With the advent of the massive postfracturing period. With the advent of the massive hydraulic fracturing (MHF) treatment in recent years, the need for new solutions for evaluating these systems has increased. The problem with the older solutions was the need for many assumptions to arrive at a simple solution. One of the more common assumptions made in these systems was the use of linear flow to describe the flow within the fracture. In gas wells with finite-conductivity fractures producing at high flow rates, the non-Darcy effect is created within the fracture. Hence, new solutions must be developed for these systems. The objective of this paper is to present a new semianalytical solution to this problem that can be applied both to the linear and to the nondarcy flow regimes within the fracture.Over the years. several methods have been developed to analyze postfracture data. Gringarien et al. first solved the fracture system analytically for three special cases: infinite-conductivity vertical fracture, uniform flux vertical fracture, and horizontal fracture. At that time, its application became quite useful. But since not all systems behaved in this manner, the need for further solutions was warranted. Cinco-L. et al. investigated the general case of finite-conductivity vertical fractures, which included the above solution. as well as fracture conductivities as low as 0.1. This research also led to the need to analyze short-time data to obtain unique solutions. Similar results were obtained by Agarwat et al., who presented a finite-difference solution to this problem, considering both the constant rate as well as the problem, considering both the constant rate as well as the constant pressure cases.One of the first papers written on the effects of non-Darcy flow in fractured systems was by Wattenbarger and Ramey. They investigated the effects of non-Darcy flow in the formation and concluded that these effects cannot be felt if the fracture is long or intermediate in size. They further concluded that the effects of turbulent flow within the fracture were more significant.Holditch and Morse investigated the effect of turbulent flow in a fracture and analyzed the transient behavior of specific conductivities (low, medium, and high), giving a qualitative approach to the solution. They stressed the need for greater detail on these solutions and showed that there was indeed a large reduction in the fracture conductivity when non-Darcy flow was included. Although Holditch and Morse gave a detailed descriptive insight into the flow regime problem, they did not develop any general methods for determining the actual conductivity of the fracture. SPEJ P. 681

Shale Reservoir Drainage Visualized for a Wolfcamp Well (Midland Basin, West Texas, USA)

“…The velocity plot (Figure 9b) reveals that the oil migrates fastest near the tips of the fractures, with an interior region between the fractures draining much slower. Classical analytical flow models [92] asserted that no fluid flow would occur from matrix into the fracture tips. Only flow of matrix normal to the fracture is assumed, which is clearly not what we see in our CAM simulations where flow near the fracture is fastest and not following sub-parallel or linear streamlines, but more complex particle paths.…”

Research for Unsteady Seepage Flow of Asymmetrical Fractured Vertical Wells in Coalbed

“…Many scholars at home and abroad have done a lot of research on this aspect [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], the domestic aspects, Wei Chen [8] established the evaluation model of finite conductivity and symmetrical fractured vertical wells in coalbed methane reservoirs; Weiping Ouyang [9] uses the finite element method to establish the numerical well test model of vertical fractured well of coalbed methane infinite conductivity, and the double logarithmic well test theory chart is drawn; Haitao Cao [13] used the theory of point source function to deduce modern decreasing plate of CBM symmetrically fractured well production; Baojun Cao [14] established a model for asymmetric fracture productivity of volcanic rocks based on the principle of conformal transformation and equivalent filtrational resistance; Wenjuan Wu [15] took the Chang 6 oil reservoir in Ordos Basin as an example, using the logging data to carry out the geological modeling and studying the three-dimensional stress field established the numerical simulation model of the asymmetric fracturing in the ultra-low permeability oil and gas reservoirs; Jian Xiong [16] derived productivity prediction model of finite conductivity asymmetric vertical fractured wells in low permeability gas reservoirs based on the steady flow theory and conformal transformation. The foreign aspects, Benjamin, J. and Barker [17] studied the pressure dynamics of finite conductivity symmetrical fractured vertical well in coalbed methane with confined boundaries based on the assumption of two dimensional single-phase Darcy flow; K.H.Guppy [18] established a numerical and semi-analytical model to analyze the high velocity non-Darcy's flow behavior of the finite conductivity fractured wells in coalbed methane reservoirs; Fernando Rodriguez [19] established a semi-analytical model of finite conductivity asymmetrical fractured well in oil reservoirs based on a new solution to the dynamic analysis of quasi-linear flow and bilinear flow pressure; B.D. Poe [20] gave a dynamic analysis model of pressure propagation in ...…”

Gas Condensate Flow Around Hydraulically Fractured Wells

“…The inertial or non-Darcy effect in HFWs has also been studied by some investigators and different correlations for the estimation of fracture skin have been introduced for these flow systems (Guppy et al 1982;Giddley 1991;Settari et al 2002;Huang and Ayoub 2007). In all these studies, the negative impact of inertia in increasing the pressure drop in the fracture, i.e., reducing effective fracture conductivity, has been highlighted.…”