It is well documented in the literature that hydraulic fracture treatments, although successful, often underperform: Frac and Pack completions exhibit positive skin values, and traditional hydraulic fracture completions show discrepancies between the placed propped length and the effective production fracture length. Ineffective fracture clean-up is often cited as a likely culprit. This paper presents some of the results of an investigation of fracture clean-up mechanisms. This investigation was undertaken under a Joint Industry Project (JIP) active since the year 2002. The data discussed builds on the initial results published in early 2006, which indicated that the polymer concentrates only in the filter cake and that flow along the fracture encounters significant yield stress when the filter cake cumulative thickness dominates the width of the fracture. The new results presented here demonstrate successful strategies that mitigate the effects of excessive filter cake thickness. Experimental data demonstrate that flow along the fracture would encounter lower yield stress when the breaker is delivered directly to the filter cake as opposed to randomly distributed. The data also indicate that a smaller breaker amount delivered directly into the filter cake is more effective at reducing the yield stress effects than a larger breaker amount delivered randomly in the slurry. Alternative breaker materials are explored and additional data are also presented to estimate the yield stress effect for fluid flow across the filter cake from the reservoir into the fracture. Introduction A Joint Industry Project (JIP), active since 2002, was created with the goal of studying fracture clean-up and using the mechanisms uncovered to devise methods that would allow the production to benefit from the full length of the fracture placed. This would either boost revenue by increasing production or decrease cost by placing smaller size treatments that would still deliver the same production as the larger, less effective treatments. It is well documented in the literature that hydraulic fractures often underperform: Frac and Pack completions exhibit positive skin values,1,2 and traditional hydraulic fracture completions show discrepancies between the placed propped length and the effective production fracture length.3 Polymer damage leading to ineffective fracture clean-up is prominent in the list of usual suspects.3–6 In addition, it was surmised that the concentrated polymer has significant yield stress and its effect on fracture fluid clean-up was modeled using a modified reservoir simulator.7,8 The production simulation indicated clearly that yield stress can result in only a fraction of the fracture length contributing to production for a long period of time. However, the existence of yield stress effect remained controversial until the first publication9 resulting from this JIP work was made at the Formation Damage Symposium in Lafayette, February 2006. In a series of lab experiments, yield stress measurements ranged from 0 - 17 Pa. This paper builds on the results published earlier9 and demonstrates successful strategies that mitigate the yield stress effects to help restore the effectiveness of the full length of the fracture. In addition, it presents the first data characterizing flow across the filter cake to simulate flow from the reservoir into the fracture as opposed to considering only flow along the fracture length.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper summarizes part of the results of an investigation of fracture clean-up mechanisms undertaken under a Joint Industry Project active since the year 2002. It is well documented in the literature that hydraulic fractures, although successful, often underperform: Frac and Pack completions exhibit positive skin values, and traditional hydraulic fracture completions show discrepancies between the placed propped length and the effective production fracture length. Ineffective fracture clean-up is often cited as a likely culprit.The main results presented in this paper were obtained using a modified conductivity cell to allow polymer concentration via leakoff, and measurements of flow initiation gradients. The paper will discuss the experimental set-up and some of the artifacts that had to be removed prior to ensuring more reliable data. The results highlight the crucial role played by the filter cake and present new data that would significantly change the common industry practice of relying simply on an average polymer concentration factor. [1][2][3] It is shown that contrary to the current method that calculates an average polymer concentration, the polymer, in practice, concentrates only in the filter cake. It is also shown that the filter cake thickness compared to the fracture thickness plays a critical role in creating significant yield stress effects, which could be either avoided through adequate design or used to estimate the resulting productivity loss.
Summary It is well documented that hydraulic-fracture treatments, although successful, often underperform. Frac-and-pack completions exhibit positive skin values, and traditional hydraulic-fracture completions show discrepancies between the placed propped length and the effective production fracture length. Ineffective fracture cleanup is often cited as a likely cause. This paper presents some of the results of an investigation of fracture-cleanup mechanisms. This investigation was undertaken under a joint-industry project (JIP) active since the year 2002. The data discussed build on the initial results published in early 2006, which indicated that the polymer concentrates only in the filter cake, and that flow along the fracture encounters significant yield stress when the filter-cake cumulative thickness dominates the width of the fracture. The new results presented here demonstrate successful strategies that mitigate the effects of excessive filter-cake thickness. Experimental data demonstrate that flow along the fracture would encounter lower yield stress when the breaker is delivered directly to the filter cake as opposed to random distribution. The data also indicate that a smaller breaker amount delivered directly into the filter cake is more effective at reducing the yield-stress effects than a larger breaker amount delivered randomly in the slurry. Alternative breaker materials are explored, and additional data are also presented to estimate the yield-stress effect for fluid flow across the filter cake from the reservoir into the fracture.
In unconventional reservoirs, the drivers of reservoir quality and hydrocarbon producibility are mostly evident at the scanning electron microscope (SEM) scale. For field applications, the practical scales of observation have resolutions from few feet to tens of feet. Finding ways of integrating the two scales allows propagation of knowledge, obtained at SEM and core scale, across the field. This is achieved via strong understanding of rock texture and composition, and of the geologic processes that defined them. The objective is to understand the rock, via detailed geologic and petrologic core studies, and define ways to identify core-scale rock texture and composition with well log and seismic measurements.We define the depositional and diagenetic transformations that occurred in the various facies of the Haynesville and Bossier system using core geologic and petrologic studies. We identify the different textural and compositional properties that define these facies and, by selecting a log suite sensitive to texture and composition, investigate their ability to discriminate these differences. We use a core-log model to predict the distribution of these geologic facies in other regions of the field, and validate these predictions with additional core studies in these regions. The potential and limitation of the log responses to identify subtle changes in rock texture and composition is critical to this effort. Once validated, the log-scale model is filtered to seismic resolution, and used to map geologic units at the seismic scale.The log-scale measurements detect sequences of the core-scale facies, thus allowing us to map their presence and distribution across the play. The method improves field geologic characterization, defines an efficient selection criterion for additional science wells with core and for selection of additional seismic data.Core-log integration was successful across a region of 7,185 square miles, and core-log-seismic integration was successful across a region of 200 square miles. The method provided a cost efficient concept for exploration, and for tying the varying geologic processes in the basin to the resulting conditions of reservoir quality and production potential. It also provided information for more effective well placement design. IntroductionSuccess in reservoir exploration and production depends on early understanding of the distribution and values of reservoir properties: porosity, permeability, hydrocarbon saturation, pore pressure, mechanical strength, and others within the region of interest. These can be readily measured, where core samples or log data exists. However, and in particular for unconventional, organic-rich mudstone plays, reservoir properties may change considerably, locally and regionally, laterally and vertically (Suarez-Rivera, 2011), and predicting their variability over the region of interest is of fundamental importance for hydrocarbon exploration. Developing a geologic model of the region is a first step for understanding the variability in the reservoi...
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