|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
In horizontal-well, plug-and-perforate completions, various studies have shown that not all perforation clusters are stimulated equally. To increase perforation cluster treatment efficiency, engineers attempt to move the perforations of each stage to similarly-stressed rock. Most of these efforts have not included predictions quantifying efficiency improvements. This paper outlines a methodology for predicting improvements of perforation cluster treatment efficiency and includes a case study verifying the results of the model using pre-treatment diagnostics.
In four Western Anadarko Basin wells, the operator measured mechanical rock properties using drill bit geomechanics. These properties were used to calculate the changes in minimum horizontal stress along each ~5,000-ft horizontal well. Within each treatment stage, the engineers chose perforation locations to minimize the difference in minimum horizontal stress. Using offset vertical logs and the geosteering interpretations, the engineers built a high-resolution fracture simulation model for each well. The model included the measured mechanical properties along the wellbore path. Comparing results from a geometric perforation model and the stress-balanced perforation model, the engineers predicted increased perforation cluster efficiencies between 10 and 20%.
The four wells were completed using the stress-balanced perforation designs. Like all previous wells in the area, the operator performed step-down rate tests on these wells before each stimulation treatment. The step-down rate test is a common hydraulic fracturing diagnostic to quantify the number of open perforations taking treatment fluid. Compared to the operator's previous geometrically-perforated wells, the wells with the stress-balanced perforation designs showed more open perforations. A higher number of open perforations suggests a greater perforation cluster treatment efficiency. The increase in efficiency measured by the step-down rate tests was consistent with the model predictions.
By understanding how stress-balancing perforation clusters will affect perforation cluster treatment efficiency, operators can optimize stimulations. The industry has not widely adopted stress-balanced perforation designs or other ‘engineered’ completion strategies. The results of ‘engineered’ completion studies have often been inconclusive, likely due to small sample sizes and reliance on production results. By combining affordable measurement of rock properties, modeled perforation cluster efficiency, and an affordable measurement of perforation efficiency, this paper provides a methodology for economically optimizing multi-stage stimulations in horizontal wells.
Robinson, Stephen (DarkVision Technologies Inc.) | Littleford, Thomas (DarkVision Technologies Inc.) | Luu, Tim (DarkVision Technologies Inc.) | Wardynski, Kacper (DarkVision Technologies Inc.) | Evans, Andrew (Jagged Peak Energy) | Horton, Blake (Encana Oil & Gas, USA) | Oman, Michael (Petronas Canada)
Abstract A new solid-state, high-resolution acoustic imaging technology has been applied in hydraulically fractured wells to image and quantify perforation erosion. The downhole device captures detailed full-lateral logs of horizontal wells, without the need for clear fluids to facilitate measurements. This paper discusses how the imaging technology functions, lab testing that validated the measurements, and field testing completed with several operators in a variety of reservoirs and basins. This high-resolution, acoustic-based downhole imaging technology provided a 360-degree view inside a variety of wells. Instead of optics, the imaging technology used high-frequency sound waves to image a full lateral through opaque fluids at sub-millimetric levels. The imaging tool was conveyed on either tractor or e-coil to continuously log the wellbore between 15 and 30ft/min, completing a full azimuthal scan that imaged individual perforations regardless of orientation. A range of imaging techniques quantified and measured each perforation to determine the extent of erosion in each perforation, cluster, and stage sustained during the hydraulic fracturing process. The acoustic imaging technology was initially tested in the lab with calibration jigs and perforated pipe samples to validate its accuracy. The technology was then field deployed by several operators and used to assess perforation erosion in extended horizontal wells by scanning the entire well from toe to heel and measuring thousands of perforations in a single log. The data gathered quantified the perforation diameter, perforation erosion range, perforation orientation dependency, cluster efficiency, perforation erosion bias, and discovered the presence of significant casing damage around areas where plugs were set. The image results showed the distribution, size, and measured diameter for each perforation in each cluster. The results noted toe or heel biases and how these changed in different well types and designs in different basins. The data allowed operators to reach conclusions regarding erosion and cluster efficiency across the entire lateral in various wells in the Montney, Permian, and Anadarko basins. Wells across North America were scanned in several other basins for comparison purposes using various completion designs from different operators. The high-resolution acoustic imaging technology offers a robust 360-degree view of long horizontal wells and perforation measurements post-fracture. Over 35,000 perforations have been measured using the technology in the field across various well types with different designs. The technology has proven to be a valuable tool in improving and optimizing completion designs by providing detailed feedback on where designs are working effectively and where they can be improved.
Ugueto C., Gustavo A. (Shell Exploration and Production) | Huckabee, Paul T. (Shell Exploration and Production) | Molenaar, Mathieu M. (Shell Exploration and Production) | Wyker, Brendan (Shell Exploration and Production) | Somanchi, Kiran (Shell Exploration and Production)
Abstract It is now well established that the production from horizontal wells completed via hydraulic fracture stimulations (fracs) is highly variable along the length of the wellbore. In addition to subsurface conditions, elements of the completion design, such as fluid volume, proppant tonnage, rate, stage length, the number of perforation clusters and their spacing, influence the performance of individual stimulated intervals and wells. Information about completion efficiency can be obtained using Fiber Optic (FO) diagnostics. Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) provide great insights into the factors controlling frac construction and performance of each perforation cluster. The integrated analysis of DAS and DTS in horizontal wells completed with multiple perforation clusters per stage indicate that, although most perforation clusters receive fluids during the stimulation, there are significant changes in efficiency during the frac stimulation process that can impact frac connectivity, conductivity and ultimately, their production. This presentation illustrates recent observations about Perforation Cluster Efficiency (PCE) using FO diagnostics and summarizes the results for many wells with Cemented Plug and Perforated completions Limited Entry design (CPnP LE).
Effective fracture treatment distribution to stimulate and obtain production from all perforation clusters is a key goal for success in unconventional reservoirs. The objectives of this work were to assess the impacts of multi-cluster stage perforating design parameters and execution uncertainties on treatment slurry distribution, production, ultimate recovery, and offset well interference for unconventional reservoirs.
A stochastic perforation breakdown and slurry injection model and a conceptual reservoir simulator were used to investigate treatment slurry distribution, production, and ultimate recovery impacts. The design parameters in the analysis were clusters per stage, cluster spacing, maximum proppant concentrations, perforation diameter, and number of perforations per cluster for both fixed- and variable-shot cluster designs. Uncertainties evaluated included perforation breakdown percentage, perforation shot phasing for non-oriented carriers, perforation hole diameter growth from erosion, and formation permeability.
As part of the analysis, the authors defined and used a new dimensionless quantity—the Slurry Distribution Number (Nsd)—that potentially fills a gap as no standard industry definition exists for perforation cluster efficiency. Nsd successfully correlated perforating design changes with slurry distribution outcomes. The authors used the results to identify strategies to mitigate uncertainty impacts, obtain more predictable outcomes, and achieve improved production results.
Novel information is presented that can assist perforating design optimization for unconventional reservoirs. In addition to introducing Nsd, the authors show perforation carrier phasing and shot phasing within the casing are generally not the same for decentralized carrier systems. The authors demonstrate how to model the perforation breakdown and stage stimulation process using a combination of published geomechanics, perforation erosion, and perforation flow resistance models. Lastly, the authors describe future study opportunities for perforating uncertainties and design parameters.
Abstract The objective of achieving uniform stimulation of a reservoir through hydraulic fracturing from a horizontal well typically depends upon the ability to generate a uniform array of hydraulic fractures from multiple entry points. However getting all the hydraulic fractures in an array to grow simultaneously is a challenge. The challenge apparently arises not only due to reservoir variability, but also in a substantial part due to the stress interaction among growing hydraulic fractures. This phenomenon, referred to as a stress shadowing, inhibits the growth of inner fractures and favors the growth of outer fractures in the array. Recently, we created a new hydraulic fracture simulator which simulates the growth of an array of hydraulic fractures in 10–10 of the computation time required for fully coupled 3D simulations of multiple parallel planar hydraulic fracture growth. Using a novel energetic approach to account for the coupling among the hydraulic fractures and through judicious use of asymptotic approximate solutions, the simulation enables designs reducing the negative effects of stress shadow by balancing the interaction stresses through non-uniform perforation cluster spacings. Furthermore, so-called limited entry approaches are thought to be capable of promoting greater uniformity among simultaneously growing hydraulic fractures as long as the number and diameters of the perforations in each cluster are appropriately designed. In order to enable such optimizations and designs, we add perforation loss into to the approximate, energy-based simulator. Our results show the potential of choosing the proper perforation diameter and number to double the fracture surface area generated by a given injected fluid volume though minimizing the negative effect of interaction. The usefulness of the new simulator is demonstrated by development of example limited entry designs and optimal spacings for different numbers of entry points.