Geomechanical behavior of the reservoir and caprock system at the In Salah CO2 storage project

Almost 4 million metric tons of CO₂ were injected at the In Salah CO₂ storage site between 2004 and 2011. Storage integrity at the site is provided by a 950-m-thick caprock that sits above the injection interval. This caprock consists of a number of low-permeability units that work together to limit vertical fluid migration. These are grouped into main caprock units, providing the primary seal, and lower caprock units, providing an additional buffer and some secondary storage capacity. Monitoring observations at the site indirectly suggest that pressure, and probably CO₂, have migrated upward into the lower portion of the caprock. Although there are no indications that the overall storage integrity has been compromised, these observations raise interesting questions about the geomechanical behavior of the system. Several hypotheses have been put forward to explain the measured pressure, seismic, and surface deformation behavior. These include fault leakage, flow through preexisting fractures, and the possibility that injection pressures induced hydraulic fractures. This work evaluates these hypotheses in light of the available data. We suggest that the simplest and most likely explanation for the observations is that a portion of the lower caprock was hydrofractured, although interaction with preexisting fractures may have played a significant role. There are no indications, however, that the overall storage complex has been compromised, and several independent data sets demonstrate that CO₂ is contained in the confinement zone.In Salah is an industrial-scale carbon capture and storage project located in central Algeria. Between 2004 and 2011, 3.8 million metric tons of CO₂ were injected into an anticlinal structure at ∼1,800 m depth. Storage integrity at the site is provided by a massive, 950-m-thick caprock that sits above the injection interval (Fig. 1). It consists of a number of low-permeability units that work together to limit vertical fluid migration. These are grouped into main caprock units, providing the primary seal, and lower caprock units, providing an additional buffer and some secondary storage capacity.Open in a separate windowFig. 1.Stratigraphic column with interval depths at well KB-502. Depth is given as meters of true vertical depth below the rotary table (m TVD brt) of the drilling rig, a common elevation datum in the oil and gas industry.In June 2011, injection operations halted at the site to allow reevaluation of the injection strategy (1). At the time, several monitoring observations suggested that pressure, and probably CO₂, had migrated vertically into the lower portion of the caprock. Although there are no indications that overall storage integrity has been compromised, these observations raise interesting questions about the geomechanical behavior of the reservoir and lower caprock system.Several hypotheses have been put forward by various groups to explain these observations. These include fault leakage, flow through preexisting fractures, or the possibility that injection pressures hydraulically fractured a portion of the lower seal (2–13). In this work, we evaluate these hypotheses in light of the available data. We suggest that the most likely explanation for the observed behavior is that the lower caprock was hydrofractured, although interaction with preexisting fractures may have played a significant role. Previous studies by Bissell and colleagues (4) and Oye and colleagues (8) have shown that injectivity and microseismic data show indications of fracturing behavior, at least in the reservoir and possibly in the overburden. Here, we use well data to constrain the state of stress in the reservoir and lower caprock, providing strong support for the hydrofracture hypothesis.This work also highlights those monitoring and analysis methods that have been most useful for understanding the field behavior, as well as lessons learned and potential improvements. This perspective can guide future carbon storage projects.     

Regression to the mean in home blood pressure: Analyses of the BP GUIDE study

The aim of our study was to estimate the size of regression to the mean with home blood pressure (BP) monitoring and compare with that for office BP. Office and home BP measures were obtained from the BP GUIDE (value of central Blood Pressure for GUIDing managEment for hypertension) study, in which 286 patients had BP measured every 3 months for 12 months. Patients were categorized by 10 mm Hg strata of baseline BP, and regression to the mean measures was calculated for home and office BP. High baseline home BP readings tended to be lower on long‐term follow‐up, and low baseline readings tended to be higher. For example, patients in the group with mean baseline home systolic BP ≥ 150 mm Hg had a mean baseline systolic BP of 156 mm Hg, which fell to 143 mm Hg at 12 months; and patients in the group with mean baseline home systolic BP < 120 mm Hg had a mean baseline systolic BP of 113 mm Hg which rose to 120 mm Hg at 12 months. Similar patterns were seen in intervention and control groups, and for diastolic BP. The regression dilution ratio for home systolic BP and diastolic BP was 0.52 and 0.64, respectively, compared to 0.40 and 0.55 for office systolic BP and diastolic BP, respectively. Home BP is subject to regression to the mean to a similar degree as office BP. These findings have implications for the diagnosis and management of hypertension using home BP.     

Utility of point-of-care biliary ultrasound in the evaluation of emergency patients with isolated acute non-traumatic epigastric pain

To determine the utility of emergency physician-performed point-of-care biliary ultrasound in the evaluation of emergency department (ED) patients with isolated acute non-traumatic epigastric pain. This was a multi-center prospective observational study of adult patients presenting to the ED with isolated acute non-traumatic epigastric pain. Patients with abdominal tenderness at any site other than the epigastric region, or with a history of gall stones, cholecystectomy, gastrointestinal bleeding, chronic abdominal pain, trauma, or altered mental status were excluded. Emergency physician investigators performed point-of-care biliary ultrasound after clinical assessment. Demographic information, history, physical examination findings, laboratory results, additional diagnostic tests, and disposition data were collected. A total of 51 patients (39 women, 12 men) were enrolled. The mean age of the patients was 36.4 years ± 13.6 (SD). All subjects had isolated epigastric tenderness. Gallstones were found in 20/51 (39 %, 95 % CI 26–52 %) on point-of-care biliary ultrasound. Of the 20 patients who had gallstones, eight had sonographic signs of chloecystitis. The treating emergency physicians’ initial evaluation did not plan to include an ultrasound in 17/20 patients with gallstones. 19/20 patients were initially given a GI cocktail by the treating emergency physicians. Point-of-care biliary ultrasound detected gall stones in more than one-third of ED patients with isolated acute non-traumatic epigastric pain. All patients presenting to the ED with non-traumatic epigastric pain should be evaluated for biliary disease with an ultrasound imaging study. Bedside ultrasound can avoid misdiagnosis and expedite management in these patients.     

Association between in-hospital acute hypertensive episodes and outcomes in older trauma patients

Although chronic hypertension is associated with long-term complications, few studies directly examine the effects of in-hospital acute hypertensive episodes in trauma patients. The aim was to determine whether there is an association between in-hospital acute hypertension and morbidity. We included trauma patients between 45 and 89 years who presented to a level I trauma center between January and September 2008. Patients were classified as either experiencing or not experiencing acute hypertensive episode(s) as defined by systolic blood pressure ≥180, or diastolic blood pressure ≥110 mmHg, or at least two readings of systolic blood pressure ≥160 or diastolic blood pressure ≥100 mmHg. The primary outcome was a composite endpoint of myocardial infarction, stroke, venous thromboembolism, new-onset atrial fibrillation, or acute kidney injury. At least one acute hypertensive episode occurred in 42.6 % (69/162) of patients. A total of 10.5 % patients developed the composite endpoint, 17.4 % in the acute hypertensive episode group compared to 5.4 % in the non-hypertensive group, p = 0.012. Patients in the acute hypertensive group were more likely to require an intensive care unit admission compared to the non-hypertensive group (33.3 versus 14.0 %, p = 0.004). Of the 17 patients who developed an acute hypertensive episode and met the primary endpoint, 10 were on home antihypertensive medications. Of those, four were restarted on all medications initially, three on some, two were started on new medications, and one was not resumed on home medications. Development of acute hypertensive episode(s) in older trauma patients was associated with an increase in the composite endpoint. Prospective studies are needed.     

Next-generation active immunization approach for synucleinopathies: implications for Parkinson’s disease clinical trials

Immunotherapeutic approaches are currently in the spotlight for their potential as disease-modifying treatments for neurodegenerative disorders. The discovery that α-synuclein (α-syn) can transmit from cell to cell in a prion-like fashion suggests that immunization might be a viable option for the treatment of synucleinopathies. This possibility has been bolstered by the development of next-generation active vaccination technology with short peptides-AFFITOPEs^® (AFF)- that do not elicit an α-syn-specific T cell response. This approach allows for the production of long term, sustained, more specific, non-cross reacting antibodies suitable for the treatment of synucleinopathies, such as Parkinson’s disease (PD). In this context, we screened a large library of peptides that mimic the C-terminus region of α-syn and discovered a novel set of AFF that identified α-syn oligomers. Next, the peptide that elicited the most specific response against α-syn (AFF 1) was selected for immunizing two different transgenic (tg) mouse models of PD and Dementia with Lewy bodies, the PDGF- and the mThy1-α-syn tg mice. Vaccination with AFF 1 resulted in high antibody titers in CSF and plasma, which crossed into the CNS and recognized α-syn aggregates. Active vaccination with AFF 1 resulted in decreased accumulation of α-syn oligomers in axons and synapses, accompanied by reduced degeneration of TH fibers in the caudo-putamen nucleus and by improvements in motor and memory deficits in both in vivo models. Clearance of α-syn involved activation of microglia and increased anti-inflammatory cytokine expression, further supporting the efficacy of this novel active vaccination approach for synucleinopathies.