ADNOC's Smart Liner Initiative – A Step-Change in Matrix-Acid Stimulation Efficiency

ADNOC is progressing with large-scale rig-less high-rate matrix stimulation by deployment of advanced lower completions. A key contribution to future production growth is expected to come from these "Smart Liners" that rely on the principles of the limited-entry technique. The concept is based on a number of small, pre-drilled and unevenly spaced holes which enable an even distribution of acid along the entire reservoir drain to be stimulated. The smart liner incorporates swellable packers to avoid annular flow of acid to preferential zones and to isolate segments with heterogeneities. In this work, we focus on aspects related to planning, design and execution of high-rate matrix-acid stimulation of wells. We demonstrate that short wells need a different design approach compared to extended-reach wells and we provide guidelines on how to achieve the highest achievable pump rate and desired acid volume subject to reservoir, well and equipment constraints. The carbonate reservoirs typically exhibit considerable variation in permeability along the well, hence techniques for production profiling, such as inline tracers, are valuable for assessing the actual stimulation effectiveness. Wormhole penetration for a particular acid system will vary depending on the rock petrophysical properties and the reservoir properties; therefore, a systematic data analytics project is on-going.

Numerical Investigation on Propagation Behaviors of a Three-Dimensional Fracture Network Coupled with Microseismicity in Fractured Shale Reservoirs

The formation mechanism and propagation behaviors of a three-dimensional hydraulic fracture network in fractured shale reservoirs remain unclear, especially when the scale of hydraulic fractures is much larger than that of natural fractures. In this study, taking the well XH in the Longmaxi shale reservoir in the Sichuan Basin, China as an example, we develop a fully three-dimensional numerical model for hydraulic fracturing coupled with microseismicity based on the discrete lattice method. We introduce a randomly generated discrete fracture network into the proposed model and explore the formation mechanism of the hydraulic fracture network under the condition that the hydraulic fractures are much larger than natural fractures in scale. Moreover, microseismic events are inversely synthesized in the numerical model, which allows the evolution of the fracture network to be monitored and evaluated quantitatively. In addition, we analyze the effects of injection rate, horizontal stress difference, and fluid viscosity on fracture propagation. Our results show that when the scale of hydraulic fractures is much larger than that of natural fractures, the fracture morphology of “main hydraulic fractures + complex secondary fractures” is mainly formed. We find that a high injection rate can not only create a complex fracture network, but also improve the uniform propagation of multi-cluster fractures and enhance far-field stimulation efficiency. Optimizing the horizontal wellbore intervals with low horizontal stress differences as the sweet spots of hydraulic fracturing is also beneficial to improve the stimulation efficiency. For zones with a large number of natural fractures, it is recommended to use an injection schedule with high viscosity fluid early and low viscosity fluid late to allow the hydraulic fractures to propagate to the far-field to maximize the stimulation effect.

Effect of Stress Shadow Caused by Multistage Fracturing from Multiple Well Pads on Fracture Initiation and Near-Wellbore Propagation from Infill Wells

Summary Multistage fracturing with multiwell pads (MSFMP) is an essential technology for the efficient development of unconventional oil and gas reservoirs, but the reservoir area between two well pads is often not stimulated. Fracture initiation and near-wellbore propagation from infill horizontal wells drilled with different azimuth from the optimal azimuth in the unstimulated area is poorly understood, largely because of the stress shadow (or induced stress) caused by MSFMP. In this study, we propose an integrated method for calculating the stress shadow caused by MSFMP and then determine optimal completion parameters for infill horizontal wells in the unstimulated connecting area between two well pads. First, we develop a theoretical stress shadow model caused by MSFMP on the basis of the dislocation theory. Considering two extreme cases, fully open and completely closed propped fractures, the range of stress shadow in the unstimulated area after MSFMP of 20 horizontal wells in Platform H of tight reservoirs in the Changqing Oilfield, China, is considered as an example. Second, we import the calculated stress shadow into a 3D perforated fracturing model that is built based on the discrete lattice method. Then, we investigate the influence of perforation technology, horizontal wellbore azimuth, phase angle, and injection rate on fracture initiation and near-wellbore propagation. Our results show that this model is capable of calculating stress shadow at any position and then can be used to optimize the fracturing interval for the middle unstimulated area. We find that appropriate perforation and fracturing parameters significantly decrease the complexity of near-wellbore fractures. The models and results presented in this paper provide a new method and new insight for quantifying and optimizing fracture initiation and propagation for infill horizontal wells to maximize reservoir stimulation efficiency.

Stimulation efficiency of an actuator driven piston at the biological interface to the inner ear

Direct acoustic cochlear stimulation uses piston motion to substitute for stapes footplate (SFP) motion. The ratio of piston to stapes footplate motion amplitude, to generate the same loudness percept, is an indicator of stimulation efficiency. We determined the relationship between piston displacement to perceived loudness, the achieved maximum power output and investigated stapes fixation and obliteration as confounding factors. The electro-mechanical transfer function of the actuator was determined preoperatively on the bench and intraoperatively by laser Doppler vibrometry. Clinically, perceived loudness as a function of actuator input voltage was calculated from bone conduction thresholds and direct thresholds via the implant. The displacement of a 0.4 mm diameter piston required for a perception equivalent to 94 dB SPL at the tympanic membrane compared to normal SFP piston displacement was 27.6–35.9 dB larger, consistent with the hypothesis that the ratio between areas is responsible for stimulation efficiency. Actuator output was 110 ± 10 eq dB SPLFF @1Vrms ≤ 3 kHz and decreased to 100 eq dB SPLFF at 10 kHz. Output was significantly higher for mobile SFPs but independent from obliteration. Our findings from clinical data strongly support the assumption of a geometrical dependency on piston diameter at the biological interface to the cochlea.

Novel Deployment of Tracers Leads to High-Confidence Results

A unique well-tracing design for three horizontally drilled wells is presented utilizing proppant tracers and water- and hydrocarbon-soluble tracers to evaluate multiple completion strategies. Results are combined to present an interpretation of them in the reservoir as a whole, where applicable, as well as on an individual well basis. The new approach consists of tracing the horizontal well(s) leaving unchanged segments along the wellbore to obtain relevant control group results not available otherwise. The application of the tracers throughout each wellbore was designed to mitigate or counterbalance variables out of the controllable completion engineering parameters such as heterogeneity along the wellbores, existing reservoir depletion, intra- and inter-well hydraulically driven interactions (frac hits) as well as to minimize any unloading and production biases. Completion strategies are provided, and all the evaluation methodologies are described in detail to permit readers to replicate the approach. One field case study with five horizontal wells is presented. Three infill wells were drilled between two primary wells of varying ages. All wells are shale oil wells with approximately 7,700 ft lateral sections. The recovery of each tracer is compared between the surfactant treated and untreated segments on each well and totalized to see how the petroleum reservoir system is performing. A complete project economic analysis was performed to determine the viability of a chemical additive (a production enhancement surfactant). Meticulous analysis and interpretation of the proppant image logs were performed to discern the cluster stimulation efficiency during the hydraulic fracturing treatments. Furthermore, comparisons of the cluster stimulation efficiency between the two mesh sizes of proppant pumped are also provided for each of the three new unconventional well completions. The most significant new findings are the surfactant effects on the wells’ production performance, and the impact the engineered perforations with tapered shots along the stages had on the stimulation efficiency. Both the right chemistry for the formation and higher cluster stimulation efficiencies are important because they can lead to increased well oil production. The novelty of this tracing design methodology rests in the ability to generate results with a statistically relevant sample size, therefore, increasing the confidence in the conclusions and course of action in future well completions.

High Resolution Acoustic Imaging of Plug Related Casing Damage in Hydraulically Fractured Horizontal Wells

While assessing post-hydraulic-fracture perforation growth using solid-state, high- resolution acoustic imaging tools, it was noted that plug failures were occurring at a high frequency. Though plug failures can be observed from hydraulic fracture surface pressure and flowrate data, the aggregate frequency, causes, and severity of the resulting erosional damage at plug locations was not previously well understood and highly speculative. The sub-millimetric three-dimensional imagery generated from high resolution solid-state acoustic tools significantly improved the industry's awareness of plug failure frequency, mechanisms of failure, and the resulting impact to stimulation efficiency. These acoustic tools helped to uncover the causes and explore possible solutions to failing plugs. This paper presents aggregate data encompassing casing wall loss at over 2700 plug locations and presents emerging trends that appear across the broader dataset. In addition, this paper showcases the usage of high-resolution acoustic imaging in two operator-specific case studies.

POSSIBILITY OF APPLICATION PULSATING ELECTROMAGNETIC FIELD IN A SAFER SOYBEAN PRODUCTION

The application of methods in the field of biophysics, such as the pulsating electromagnetic field (PEMP) to biological organisms, many studies are performed that indicate specific changes and efficient action on various biochemical processes of cells in plants. The obtained results do not depend only on the plant species, but also on the climatic conditions, agrotechnical measures and exposure time, intensity and nature of the fields used in the research. The aim of the study was the effect of stimulation of soybean seeds with PEMP. Soybean seeds are rich in quality proteins, oils and fats. The three-year research period 2013-2015 implied different agrometeorological conditions. Soybean seeds of the Valjevka variety were used. Soybeans were grown with different amounts of organic granular poultry manure (control – no fertilization, 750 kg.ha-1 i 1300 kg.ha-1). Seed stimulation was performed before sowing with PEMP low frequency 15 Hz and exposure of 30 minutes. Seed stimulation efficiency was very pronounced because it statistically significantly (p <0.01) increased grain yield by 4.85% and protein content in grain by 3.52%.