Vertical Fracture Height-Its Effect on Steady-State Production Increase

Abstract

Data taken from a steady-state electrolytic model have been used to developcurves showing production increase as a f unction of fracture height, fracture length, reservoir height, drainage radius, fracture flow capacity, formation permeability and wellbore radius. The work allows a fullerevaluation of the effect of fracturing parameters on productivityincrease. Introduction Hydraulic fracturing methods for productionstimulation have become a common procedure in the oiland gas industry. Fracturing treatments areperformed on wells of various potentials to help increasethe production rate. In addition to the desire forincreased production is the need to predict whatincrease might be expected. This knowledge is usefulin economical treatment planning to accomplish thedesired production goals for the well. Theoretical production increases due to horizontalradial fractures may be calculated using equationsdeveloped from mathematical analyses and electricalmodels. It also is possible to predict theoreticalproduction increases due to vertical fractures usingcurves developed from electrical and mathematicalmodels." However, these studies assumed that thevertical fracture height and the formation height wereequal, which may not be true." In addition, the finalfracture height through which fluid is produced maynot be equal to the created height. The development of vertical fracture proppanttransport relationships has made unrealistic theassumption that propped fracture height is equal tocreated fracture height. Through the use of publishedproppant transport equations, it is possible tocalculate the height of a bed of propping agent depositedin a fracture of a given height. Assuming that thefluid flowing in the fracture moves through only thepropped portion of that fracture (i.e., that theunpropped part of the fracture heals) it becomesessential to know how production increase varies with theratio of propped fracture height to formation height. It should be recognized that future investigationmay determine that the fracture does not healcompletely and that a highly permeable channel existsover the deposited bed of proppant. The effect of thischannel was not considered for the present study. The following analysis of experimental dataallowed development of curves to determinetheoretical production increases considering fracture heightas a variable. Discussion In designing a fracturing stimulation treatment anumber of variables must be considered. The size ofthe treatment, type of proppant used, proppantconcentration, treatment fluid properties and wellconditions are all factors affecting the dimensions andpermeability of the fracture. Production increase due to a vertical fracture isaffected by propped length, height, width andpermeability of the fracture for a given set of formationconditions. Production increase may be defined asthe ratio of production rate after fracturing to theproduction rate before fracturing at the samepressure differential, pe - pw. JPT P. 633ˆ