Extended-Time Conductivity Testing of Proppants Used for Multi-Stage Horizontal Completions

The American Petroleum Institute Recommended Practice 19-D (2018) is the current industry standard for conductivity testing of proppants used in hydraulic fracturing. Similar to previous standards from both the API and ISO, it continues the practice of measuring a "reference" long-term conductivity after 50-hours of time at a given stress. The fracture design engineer is then left to estimate a damage factor to apply over the life of the well completion based on correlations or experience. This study takes four standard proppants used for multi-stage horizontal well completions in North America and presents test data over 250-days of "extended-time" at 7,500 psi of effective stress. The API RP 19-D procedure was followed for all testing, but extended for 250-days duration for the four proppant types: 40/70 mesh mono-crystalline "White" sand, 40/70 mesh multi-crystalline "Brown" sand, 100 mesh "Brown" sand, and 40/70 mesh Light Weight Ceramic (LWC). The 7,500 psi stress condition was chosen to replicate initial stress conditions for a 10,000 feet deep well with a 0.75 psi/ft fracture gradient - typical of unconventional resource plays such as the Bakken formation of North Dakota or the Delaware Basin in west Texas. Results presented provide a measure of the amount of damage occurring in the proppant pack due to time at stress. To the authors’ knowledge, there has never been any extended-time conductivity data published for multiple proppant types over the timeframe completed in this study - despite the obvious need for this understanding to optimize the stimulation design over the full life of the well. Results for the four proppant types are presented as conductivity curves as a function of time for the 250-days of testing. Pack degradation is shown to follow a semi-log decline. Late time continued degradation for all materials is extrapolated over the life of a typical well (40 years), and compared to extended-time particle size distribution and crush data to explain the results observed. Extended-time data such as this 250-day study have never been published on proppants such as these despite the fact that fracture conductivity has a major impact on the productive life of a well and the ultimate recovery of hydrocarbons from the formation. The data presented should be of great interest to any engineer involved with completion designs, or reservoir engineers assessing the productive life and ultimate recovery in the formation since economic optimization is primarily driven by the interplay of fracture length/area with extended-time in-situ fracture conductivity.

The Impact of Extended-Time Proppant Conductivity Impairment on the Ultimate Recovery from Unconventional Horizontal Well Completions

The stimulation design of hydraulically fractured wells has always pitted the engineer's capability to maximize the fracture extent (or fracture half-length within the formation) versus the conductivity of the fracture pack generated by the deposited proppant material. In essence, the area of productive reservoir rock contacted by the hydraulic fracture treatment needs to be appropriately engineered to remain connected to the wellbore over the life of the well to maximize reservoir recovery. The completion design of multi-stage hydraulically fractured horizontal wells has been driven by their application to unconventional oil and gas reservoirs. This has primarily occurred in North America where most of the wells drilled and completed were operated by small, private, or upstream-only independent public companies. Metrics used to evaluate performance and completion design changes were short-term in nature and typically focused on parameters such as peak-month production, 90- or 180-day cumulative production; or at longest, the first year or two of cumulative production. Capital efficiency, and capital return or well payout were drivers of value creation in an environment where the well inventory was viewed as extensive if not unlimited and the quick recycling of invested capital created the illusion of value creation. Short-term performance metrics give credence to fracture designs that value most the early-time production that is dominated by rate acceleration. The work presented in this paper shows a comparison of fracture designs in deep unconventional formations looking to minimize cost by pumping all sand proppants versus a focus on ultimate recovery from the reservoir with designs that are more applicable to the stress regime. The work shows the importance of maintaining the wellbore connectivity to the reservoir by designing fracture treatments using proppant conductivity decline data measured over an extended-time period of months or years to maximize ultimate recovery from the reservoir. This approach will be critical to those E&P companies who view their well inventory or resource base as finite and consequently place a priority on maximizing recovery from the reservoir.

Population Dynamics of Escherichia coli Causing Bloodstream Infections over Extended Time Periods

Escherichia coli is a leading cause of community-acquired and health care-associated bloodstream infections (BSIs) worldwide. Limited information is available regarding the changes in population dynamics of human E. coli over extended time periods, especially among nonbiased E. coli isolates in large well-defined geographical regions.

Real-World Cost-Effectiveness of Late Time Window Thrombectomy for Patients With Ischemic Stroke

Background: To compare the cost-effectiveness of providing endovascular thrombectomy (EVT) for patients with ischemic stroke in the >4.5 h time window between patient groups who met and did not meet the perfusion imaging trial criteria.Methods: A discrete event simulation (DES) model was developed to simulate the long-term outcome post EVT in patients meeting or not meeting the extended time window clinical trial perfusion imaging criteria at presentation, vs. medical treatment alone (including intravenous thrombolysis). The effectiveness of thrombectomy in patients meeting the landmark trial criteria (DEFUSE 3 and DAWN) was derived from a prospective cohort study of Australian patients who received EVT for ischemic stroke, between 2015 and 2019, in the extended time window (>4.5 h).Results: Endovascular thrombectomy was shown to be a cost-effective treatment for patients satisfying the clinical trial criteria in our prospective cohort [incremental cost-effectiveness ratio (ICER) of $11,608/quality-adjusted life year (QALY) for DEFUSE 3-postive or $34,416/QALY for DAWN-positive]. However, offering EVT to patients outside of clinical trial criteria was associated with reduced benefit (−1.02 QALY for DEFUSE 3; −1.43 QALY for DAWN) and higher long-term patient costs ($8,955 for DEFUSE 3; $9,271 for DAWN), thereby making it unlikely to be cost-effective in Australia.Conclusions: Treating patients not meeting the DAWN or DEFUSE 3 clinical trial criteria in the extended time window for EVT was associated with less gain in QALYs and higher cost. Caution should be exercised when considering this procedure for patients not satisfying the trial perfusion imaging criteria for EVT.

An Electrochemically Activated Nanofilm for Sustainable Mg Anode with Fast Charge Transfer Kinetics

Highly reversible Mg plating/stripping is key for rechargeable Mg batteries and has typically been successfully demonstrated using transient electrochemical techniques such as cyclic voltammetry measurements. However, little effort has been invested in studying the stability of the electrode/electrolyte interface over an extended time. We report here the development an in situ generated surface film for Mg anodes based on electrodeposited bismuth (E_Bi). This film improves the interfacial stability of Mg in contact with the electrolyte, particularly over an extended time, and possesses fast charge-transfer kinetics (< 30 Ω∙cm2) and low non-time-sensitive interfacial film resistance (ca. 5 Ω∙cm2) for active Mg species.

Experimental simulation of proppant permeability in hydraulic fracturing at extended time under bottom-hole conditions

During hydraulic fracturing treatment, huge quantities of gel are pumped into the formation to initiate the fracture, maintain it open and transport the proppant. The fracture dimensionless conductivity (Fcd) is a key parameter to optimize the fracturing design, to estimate the productivity Index (PI) and the folds of increase (FOI). However, these parameters are affected by the gel residues which decrease the fracture conductivity; thus, the proppant cleanup is a very important step to avoid additional damage caused by fracturing fluid due to high gel concentration and the extended time of gel staying in the fracture before cleanup. Throughout the life of Hassi Messaoud, Algeria field, hydraulic fracturing technique has been aggressively used mainly in four producing formations in the Cambrian, with hard formation characteristics, an average permeability range and low reservoir pressure (0.15–0.45 psi/ft) and high stress value between 6000 and 9000 psi. In this paper, an experimental simulation is applied using a self-made cell to determine the effect of different parameters on the fracture conductivity under various bottom-hole conditions where different variables were used: effect of Proppant type, guar gel concentration, temperature, breaker concentration and closure pressure at extended time. An important drop in fracture conductivity was observed varied between 10 and 80% under stresses at interval of 2000 psi and 8000 psi, gel concentration up to 200 lb/1000 gal at extended time and temperature.

Abstract 1122‐000190: Persistent DWI Signal for 18 Months in Ischemic Stroke Patient with Carotid Web

Introduction : Diagnostic tools for acute ischemic infarcts include the use of DWI sequence on MRI to identify acute infarcts is especially useful since lesions can become hyperintense on this sequence very rapidly (Albers 1998). Over the next 15 days, DWI hyperintensity slowly decreases back to isointense. In some patients, however, there is persistent DWI hyperintensity past 1 month. There are theories that these persistent areas exhibit delayed onset infarct, prolonged ischemia, or perhaps different repair processes (Rivers, et al 2006). To this day, all DWI signals have been known to resolve within a few months even for persistent hyperintensities (Rivers, et al 2006). Carotid webs are a rare form of fibromuscular dysplasia that protrudes from the intimal tissues of carotid arteries. They are shelf‐like projections that grow into the lumen and disrupt normal blood flow (Zhang, et al 2018). These outgrowths are theorized to lead to ischemic strokes due to flow stasis and subsequent embolization of clots that form (Zhang, et al 2018). There is no consensus on the best management of carotid webs, and secondary prevention of recurrent strokes range from medical management to carotid stenting. Methods : This is a case report, and information for the patient was gathered through review of medical records on the EMR. Results : We present a case of ischemic stroke in the right basal ganglia/corona radiata, who presented with left sided weakness. The patient was found to have prediabetes, HTN, and HLD. However, she had recurrence of her symptoms over the next 18 months (figure 1). Repeat MRIs showed persistent DWI hyperintensity that slowly decreased in size and signal intensity over this period but in the same area as the initial infarct. The rest of the work up was only significant for a carotid web in the right internal carotid artery identified on conventional angiography. Ultimately she was managed with medical therapy including aspirin, statin, and antihypertensives. Conclusions : It is unclear whether the carotid web is associated with persistent DWI for such an extended time frame. There is very little research that explores the pathophysiology of ischemic strokes from carotid webs. In addition, there is even less information about the physiology of an evolving infarct that shows persistent DWI signals for such an extended time frame. Further studies that look into carotid webs may help us understand the best long term management in such patients. Future studies that explore the physiology of ischemic strokes that show such persistent DWI signals may elucidate and perhaps expand upon current management options and possibly identify new areas for intervention.

Using group sizes to optimise archery equipment

One method used by archers and coaches to optimise archery equipment is to measure the size of arrow groups on the target prior to and following an adjustment. The group sizes are then used to determine if an equipment change assisted or detracted from the archer’s performance. A model based on a Monte Carlo method and group size measurements from seven elite archers were used to test the validity of this process. The results showed that this method was neither an effective method nor useful process because the probability of false positives or false negatives was too great. A better approach to optimise archery equipment is to monitor the archer’s skill level or average score over an extended time following any change.