Nonplanar Fracture Propagation From a Horizontal Wellbore: Experimental Study

Abstract

Summary This paper presents experimental results related to hydraulic fracturing of a horizontal well, specifically the nonplanar fracture geometries resulting from fracture initiation and propagation. Experiments were designed to investigate nonplanar fracture geometries which were categorized as: multiple parallel fractures, T-shaped fractures, and reoriented fractures. This paper discusses how these nonplanar fractures can be responsible for premature screen out and excessive treatment pressure when a horizontal well is hydraulically fractured. Reasons for unsuccessful hydraulic fracturing treatments of a horizontal well are presented and recommendations to ensure clear communication channel between the wellbore and the fracture are given. Fracture initiation pressure is a function of the wellbore orientation relative to the maximum horizontal stress. It is maximum when the horizontal well is drilled in the direction of the minimum horizontal stress. Extension pressure, however, shows little variation with respect to the wellbore direction. Experimental data shows that a relationship between breakdown pressure and wellbore orientation exists and can be used for wellbore stability problems. Microfrac analysis has been applied on the experimental data and showed that care must be exercised to determine closure pressure from a microfrac test performed on a horizontal well. A new phenomenon, "Relief in Pressure (RIP)", is presented to help determine the fracture azimuth relative to the wellbore from observing the pressure behavior after breakdown. The results of these openhole experiments can also be used for perforation design in cased holes to obtain a successful hydraulic fracturing treatment. Optimum perforated interval length and perforation phasing should follow the fracture azimuth at the wellbore as ft initiates from a given horizontal well. Introduction Horizontal wells have been drilled to increase the effective drainage area as compared to a vertical well, which can penetrate a smaller portion of the same reservoir. A horizontal well is fractured to improve productivity. Fracturing a horizontal well has sometimes been a dilemma during the last few years with occurrence of premature screenouts and high treatment pressures. This work identifies some of the problems, and suggests some solutions. In most geological formations, the orientation angle of a horizontal well from the maximum horizontal stress plays a crucial role in achieving a successful stimulation treatment. The following three mechanisms related to wellbore orientation relative to the maximum horizontal stress (orientation angle), need to be addressed.Fracture-wellbore communication area. Two extreme cases, longitudinal and orthogonal fractures, provide maximum and minimum communication area between the wellbore and propagating fractures.Fracture geometry near the wellbore. Important factor that may cause early screenouts. Several different fracture geometries can result when a horizontal well is fractured, among which are multiple fractures, T-shaped fractures, and complex fractures.Fracture tortuosity near the wellbore.

Link-up of mini-fractures from perforated holes

“…The rough fracture opening surface and the failure of a mini-fracture linkup from deviated wellbores were reported by Hallam and Last [6], Veeken et al [7], Weijers and de Pater [8]. The propagation of a hydraulic fracture from oriented perforation was also studied experimentally by El Rabaa [9] and Abass et al [10,11]. The experimental observation is in general consistent with the analytical results presented in this section.…”

“…Equation (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) can then be rearranged in terms of the dislocation density parameter A n as follows:…”

Measurement and Analysis of Full-Scale Hydraulic Fracture Initiation and Reorientation

“…This reorientation results in a tortuous and segmented fracture path, as evidenced by pressure losses that can be interpreted from the injection pressure records (Weijers et al 1994). Specifically, the large pressure losses are reflected in the drop in pressure that occurs at shut-in (Abass et al 1996) and by direct measurement of the difference between the injection pressure and the pressure in the fracture measured by an offset monitoring borehole. Lecampion et al (2013) provide a concise summary of the literature dealing with reorienting hydraulic fractures.…”

Numerical analysis of the material parameter effects on the initiation of hydraulic fracture in a near wellbore region

“…Since the hydraulic fracturing procedure is a flow-deformation coupling process, the fluid flow changes the stress state in rock and the stress reversely influences the fluid flow. The major difference of this pore pressure from the bottom hole pressure obtained in the field (Jeffrey et al 1995), or indoor experiments (Abass et al 1996), is that there is a sudden increase and it slightly drops to a stable value. This is because it is the real time pore pressure simulated within the rock and exhibits a different phenomenon (Ji et al 2009, Morgan et al 2015.…”