Comparative assessment of mechanical and chemical fluid diversion techniques during hydraulic fracturing in horizontal wells

The application of fluid diversion during hydraulic fracturing is an evolving technology and has become popular amongst E&P operators over the past few years.The primary objective of the fluid diversion is to improve hydraulic fracturing treatment by increasing stimulated reservoir volume and improving hydrocarbon recovery.This is possible by achieving any of the following objectives:creating uniform distribution of treatment slurry within the target zone;treating unstimulated and under-stimulated zones;or by increasing fracture density by creating a complex fracture network.The fluid diversion application is also helpful in decreasing the number of stages(by increasing stage length)for multi-stage plug-n-perf(PnP)fracturing treatment.It is also applied to prevent fracture-driven interactions between adjacent wells,which is currently a major issue,especially in shale.In addition,for successful refracturing treatment,the diverter application is essential for isolating the existing fractures and redirecting the treatment slurry to the desired unstimulated zones.The diversion methods can be broadly categorized into the mechanical and chemical diversion.Several established mechanical diversion techniques are frac plugs,expandable casing patches,expandable liners,swellable packers,straddle packer assembly,sand plugs,frac sleeves,perforation ball sealers,and limited entry technique.The different chemical diversion techniques are particulates,fibers,gels,surfactants,perforation pods,and composite diverting.This paper describes the current status of established mechanical and chemical diverter technologies and examines their comparative advantages and challenges.Various techniques are suitable for diverter application,but the technique is selected based on the desired objective and conditions of the wellbore and reservoir.The general guidelines for selecting diversion techniques and operational considerations are also provided in the paper.The diagnosis of diversion treatment plays an essential role in diversion technique selection and optimization of selection parameters for the subsequent treatments.Therefore,the application of conventional surface pressure monitoring techniques and advanced diagnostic tools to evaluate diversion effectiveness are briefly described.Presently no standard laboratory testing method is established for the performance evaluation of diverting agents.Therefore,researchers have implemented various laboratory methods,which are briefly summarized in the paper.Significant insight into the diversion technology and guidelines for its selection and successful implementation is provided to help engineers to increase the effectiveness of hydraulic fracturing treatments.The limitations of individual diversion techniques are clarified,which provide the future scope of research for improvement in various diversion technologies.

Concomitant achondroplasia and Chiari II malformation: A double-hit at the cervicomedullary junction

We report the first case of a neonate with concurrent Chiari II malformation and achondroplasia. Although rare, both these conditions contribute to several deleterious anatomical changes at the cervicomedullary junction and thus predispose to acute hydrocephalus. Although our patient was initially asymptomatic, hydrocephalus ensued several weeks after birth and required cerebral spinal fluid diversion. We discuss the potential links between the two conditions, the pathophysiology, and the important clinical implications for the management of the increased risk of hydrocephalus.

Shunting,optic nerve sheath fenestration and dural venous stenting for medically refractory idiopathic intracranial hypertension:systematic review and meta-analysis

Background:Cerebrospinal fluid(CSF)-diversion procedures have traditionally been the standard of treatment for patients with medically refractive idiopathic intracranial hypertension(IIH).However,dural venous sinus stent(VSS)placement has been described as a safe and effective procedure for the management of medically refractive IIH.We performed a meta-analysis comparing outcomes and complications of CSF-diversion procedures,VSS and optic nerve sheath fenestration(ONSF)for the treatment of medically refractive IIH.Methods:Electronic searches were performed using six databases from 1988 to January 2017.Data was extracted and meta-analysed from the identified studies.Results:From 55 pooled studies,there were 538 CSF-diversion cases,224 dural venous stent placements,and 872 ONSF procedures.Similar improvements were found in terms of postoperative headaches(CSF vs.VSS vs.ONSF:84%vs.78%vs.62%,P=0.223),papilledema(CSF vs.VSS vs.ONSF:71%vs.86%vs.77%,P=0.192),whilst visual acuity changes favored venous stenting(CSF vs.VSS vs.ONSF:55%vs.69%vs.44%,P=0.037).There was a significantly lower rate of subsequent procedures with venous stent placement(CSF vs.VSS vs.ONSF:37%vs.13%vs.18%,P<0.001),but other complication rates were similar(CSF vs.VSS vs.ONSF:13%vs.8%vs.14%,P=0.28).Subgroup analysis of lumbar-peritoneal vs.ventriculoperitoneal shunts found no differences in symptom improvements,complications and subsequent procedure rates.Conclusions:Our findings suggest that dural venous sinus stenting may be a viable alternative to traditional surgical interventions in patients who are refractory to medical treatment.