Hydraulic Fracturing to Successfully Exploit Depleted Gas Reserves: A Case History from the North Sea

Hydraulic fracturing has been well established in the Southern North Sea (SNS) since the mid-1980s; however, it has typically been conducted as the final phase of development in new gas fields. One of these fields is Chiswick located in the Greater Markham area 90 miles offshore UK in 130 ft of water. Following an unsuccessful well repair of the multi-fractured horizontal well C4, it was decided to cost-effectively and expediently exploit the remaining pressure-depleted reserves near the toe via a single large fracture initiated from a deviated sidetrack wellbore designated C6. A deviated wellbore was chosen versus the original near-horizontal well to reduce well risk and costs and ultimately deliver an economic well. Several key challenges were identified, and mitigating measures were put in place. Modular formation dynamics tester data from the sidetrack open hole indicated the reservoir pressure gradient had depleted to 0.23 to 0.25 psi/ft, raising concerns about the ability of the well to unload the fluid volumes associated with a large fracture treatment. Wellbore deviation and azimuth with the associated potential for near-wellbore tortuosity would drive a typically short perforation interval (i.e., 3 ft). However, a compromise to mitigate convergent pressure loss in depletion was required, and the perforation interval was therefore set at 14 ft with provision made for robust step-down tests (SDT) and multi-mesh sand slugs. To further offset any near-well convergence pressure drop during cleanup, an aggressive tip screenout (TSO) proppant schedule, including a high concentration tail-in (12 PPA) with an aggressive breaker schedule, was executed to fully develop propped hydraulic width. Following formation breakdown and SDT to 40 bbl/min, the well went on near-instantaneous vacuum. Clearly, an extremely conductive feature had been created or contacted. However, upon use of a robust crosslinked gel formulation and 100-mesh sand, the bottomhole and positive surface pressure data allowed a suitable fracture design to be refined and placed with a large width, as evidenced by the extreme 2,309-psi net pressure development over that of the pad stage while placing 500,500 lbm of 16/30 resin-coated (RC) intermediate strength proppant (ISP) to 12 PPA. Although a lengthy nitrogen lift by coiled tubing (CT) was planned, the well cleanup response in fact allowed unaided hydrocarbon gas flow to surface within a short period. The well was then further beaned-up under well test conditions to a flow rate of approximately 26 MMscf/D under critical flowing conditions with a higher bottomhole flowing pressure than that of the original C4 well. Given the last producing rate of the original multiple fractured horizontal wellbore was 27 MMscf/D at a drawdown of 1,050 psi through two separate hydraulic fractures, then the outcome of this well was judged to be highly successful and at the limit of predrill expectations. This case history explains and details the rationale, methods, and techniques employed in well C6 to address the challenge of successful hydraulic fracture stimulation in a depleted formation. Challenges were addressed by combining a number of techniques, coupled with field experience, resulting in a highly productive well despite the relatively low reservoir pressure coupled with a limited time frame to plan and execute. These techniques are transferrable to other offshore gas fields in the region where reservoir depletion makes economic recovery difficult or indeed prohibitive.

Case History for the Pediatric Eye Examination

The art of taking a patient's case history is essential for a solid understanding of pertinent details before proceeding with an examination. While establishing rapport with the patient, the clinician should ask questions about birth history, developmental history, educational and social history. Active listening skills and flexibility of the provider are useful tools for an effective start to the examination. This chapter reviews categories of questions needed for optimization of case history for the pediatric patient. This includes questions focused on specific age categories, including infants and toddlers, preschoolers, elementary-aged children, and adolescents. The chapter author provides clinical pearls for a more efficient and effective exam, including a section on assisting children with special needs.

First Successful Run of 17.5 Inch Hybrid Bit in ADNOC Onshore to Drill Deviated Section

In the onshore drilling operation the main objective is always finding ways to optimize cost and improve the efficiency of drilling operations. Among the various available option, one possibility was to drill 17.5" deviated section in one run through the interbedded formation, which cause high vibrations and risk of twist-off. This section previously was drilled with minimum 2-3 bit runs for a heavy casing design. This would definitely reduce the well duration and cost. The plan involved to drill 17.5" deviated section using rotary steerable system using hybrid bit technology. Recent advances in drilling bit design has proved to be very effective in drilling surface hole sections but are limited to drill vertical holes and require multiple runs to complete a section. Special design and cutting structure is required when it comes to drill deviated hole. One supplier has combined the traditional design and come up with hybrid bit structure to achieve this goal of drilling surface deviated hole in one run. This special hybrid bit, drilled successfully 17.5" deviated section in one run with enhanced ROP by 40% compared to previous wells. This saved additional trips to change bit and avoided any stuck pipe and twist off. This kind of strategy has helped to maximize average ROP of 64 ft/hr for the entire section. The main element in optimizing the performance of is the systematic approach towards the bit selection, hydraulics and mud parameters. Outcome of this optimization resulted in case history data which shows that this kind of hybrid bit technology can be used to drill deviated wellbore with better penetration rates, lesser washouts and longer on-bottom time. This technical paper describes the results of first well drilled by a service provider using hybrid bit technology with rotary steerable system in one run. This has resulted in increasing the rate of penetration for the 17.5" deviated top hole section. Applying this kind of hybrid bit technology has not only enhanced the ROP but also helped to save rig days and cost.

Low Cost Plug and Abandonment with Hybrid Hydraulic Pulling Unit

Plug and Abandonment (P&A) operations with conventional Hydraulic Workover Unit (WHU) have an enormous benefit and impact on low-cost P&A campaign in Malaysia compare with using conventional drilling rig. Subsequently, this Hybrid Hydraulic Pulling Unit (HHPU) was the first successful deployed and safely delivered for P&A campaign together with conductor removal in offshore West Malaysia. This paper presents case study that showcase the capability of HHPU for low-cost permanent P&A campaign by eliminate requirement for additional bringing rigging-up and rigging-down of casing jack unit for conductor removal operation. The unit manage to cut and pull-out the existing completion strings, setting cement plugs, cut and pull-out multiple strings of casing along with retrieving the 24″ conductors delivering the most advantageous outcome for P&A campaign safely, efficiently and cost effectively. It was invented from 340K HWU with improvise features that capable of pull-out existing completion string and removal of the conductor with size up to 36″. This paper demonstrates a unique combination of techniques and equipment of a successfully low-cost P&A operation with excellent client satisfaction with no incident and accident were recorded. The end results may contradict traditional P&A methods, but the case history can be used for future reference or potential replication in South East Asia region.

Unreliable Semiology from Frankenstein to Freud

Examining how prose fiction and the case history share certain formal features, this chapter turns to the medical field of semiology to investigate how the Romantic-era case history models a diagnostic reading practice that extends from medicine to the novel. Mary Shelley’s Frankenstein (1818) is a notable, even parodic, literary case history informed by conventional protocols of medical reporting, visible both in Romantic-era case histories, and, at the end of the nineteenth century, in the case histories of Sigmund Freud. The Romantic case history captures fundamental tensions between the physician’s scientific report and the patient’s autobiography, which compromise the physician’s ability to trace a semiotic relationship between external symptom and underlying condition. The case history proves to be a site of disciplinary quarrel between literature and medicine: not only does it anticipate many of the epistemological problems that attend our modern attempts to read “symptomatically” or “deeply,” it also interrogates the notions of authority, personhood, and normality that continue to sustain modern medical discourse and literary criticism. As the case history reveals the unreliability of the diagnostician’s production of narrative, it also shows the limitations of interpretation in the emergent medical and literary fields of semiology.