A study of 90 wells perforated with the tubing conveyed perforating system has found a correlation between underbalance pressure and formation permeability that can be used to achieve clean perforations. The data are from gas and oil producers in clean sandstones. Data for the report are from wells which were perforated, tested, acidized, and retested. There is a clear minimum underbalance line separating the data sets of wells that had clean perforations (unassisted by acidizing) from those wells that showed a significant productivity increase after acidizing. The study includes data from oil and gas wells in the Gulf of Mexico, Louisiana (Tuscaloosa), New Mexico (Morrow), Rocky Mountain Overthrust, and Alberta, Canada. Introduction Underbalance perforating or perforating the pressure in the wellbore lower than the pressure in the formation is generally acknowledged to be one of the best methods for creating open, undamaged perforations. During the few microseconds that it perforations. During the few microseconds that it takes a shaped charge perforator to create a perforation, a focused pressure wave punches a hole through the casing and into the formation. The material in the path of the pressure wave is thrust aside and the path of the pressure wave is thrust aside and the part of the formation next to the perforation may part of the formation next to the perforation may be compacted. The resultant crushing of the formation next to the perforation can reduce the initial permeability by 70% or more. Several authors have permeability by 70% or more. Several authors have noted the presence of the crush zone surrounding the perforation and have recognized that it accounts for a large part of the damage that may inhibit production. Historically, acid breakdowns were commonly used to remove this permeability damage or reduce its effect. In underbalance perforating, the pressure differential from the formation to the wellbore helps remove this crushed formation from the perforation more successfully than perforation washing or surging. The pressure differentials necessary to remove damage from a perforation is affected by pressure and flow rate. The pressure differentials necessary for perforation cleanup usually range from approximately 500 psi to over 4000 psi and have been established by trial and error in each field. This study uses information from 90 wells that were underbalance perforated, tested, acidized, and retested. The intent of the research was to determine the minimum underbalance pressure necessary to achieve undamaged perforations. It is important to optimize the amount of underbalance pressure since excessive underbalance pressure, particularly where the cement or the formation is weak, can cause the casing to collapse or the formation to disaggregate. Discussion Tubing Conveyed System One of the most popular systems for inward differential pressure perforating is the tubing conveyed system that was first described in 1975. The system involves running a perforating gun on tubing with a packer above the gun. Underbalance pressure can be achieved by swabbing or jetting out the completion fluid in the tubing to any desired height. After the packer has been set, the gun is fired either by dropping a bar, a battery pack, or by pressure firing. A perforated nipple below the pressure firing. A perforated nipple below the packer allows the formation fluids to flow into the packer allows the formation fluids to flow into the tubing after perforating. Figure 1 is a record of bottomhole pressure during underbalance perforating. The data were collected with a bottomhole pressure recorder positioned immediately above the packer. The device positioned immediately above the packer. The device communicated with the tubing through a small port.

Differential movement in permafrost terrain due to ground freezing or thawing challenges the reliability of buried pipelines proposed for transporting natural gas from Prudhoe Bay and the Mackenzie Delta. Arctic pipelines designed to operate at conventional pressures (that is, below 10 MPa) are susceptible to wrinkling, bulging, and ovalling due to the differential movements they cause at interfaces between frozen and unfrozen ground and between different types of soil. Arctic pipelines designed to operate at superhigh pressures—defined here as pressures above 25 MPa—can accommodate the differential movements. A fair comparison between large diameter artic pipelines with operating pressures in the range from 10 to 42 MPa was made by accurately simulating flow performance with Greenpipe’s PipeCraft™ software. For any given design flow, superhigh pressure dense phase pipelines have smaller diameters and thicker walls, making them more flexible and better able to handle differential movements. And at superhigh pressures, Joule-Thomson cooling is negligible so that flowing gas stays close to ground temperature, reducing potential for frost heave or thaw settlement in the first place. Although weight per meter of superhigh pressure pipelines is similar to conventional pressure pipelines of similar flow capacity, increased flexibility means they are easier to lift and handle during construction. They also conform more easily to the terrain, resulting in less excavation and less pipe bending to make them fit the contours of the trench. The net result is reduced construction costs. When construction, maintenance and reliability are factored into the selection process, superhigh pressure dense phase pipelines provide a cost effective option for handling the challenges of arctic environments.

Abu Dhabi has been importing natural gas for domestic consumption since 2007 and at the same time has been injecting natural gas into producing oilfields for reservoir management and sequestration. An opportunity exists to inject CO2 instead and release valuable supplies of natural gas for other uses while reducing greenhouse gas emissions. CO2 suitable for injection will be available as part of Masdar’s Carbon Capture and Storage (CCS) project which will capture wet CO2 at atmospheric conditions from industrial plants and facilities, dehydrate it, compress it, and transport it by pipeline to producing oilfields for injection. This paper presents options for dehydrating and compressing CO2 to achieve the optimum result while meeting all technical requirements. Technical and economic aspects of CO2 water content specification are analyzed and discussed along with current international practices. It focuses on challenges faced by the design team in developing water content specifications and selecting dehydration technology and methods for the Masdar CCS project. Dense phase CO2 exhibits retrograde water condensation behaviour at pressures and temperatures used for pipeline transportation and injection. This means that CO2, unlike natural gas, can carry more water rather than less as pressure increases. Other products such as natural gas do not share this property with CO2 at pipeline operating conditions. Pipelines in hot countries such as the United Arab Emirates (UAE) operate at higher temperatures than pipelines in North America and Europe and this enables them to carry product containing more water without it condensing. Therefore allowable water content specifications established by the pipeline industry in North America and Europe are unnecessarily restrictive for pipelines in hotter countries. Retrograde water condensation in dense phase CO2 combined with higher pipeline operating temperatures in the UAE and other hot countries, permits higher allowable water content for pipelines carrying CO2 than is typical in other parts of the world. The specification of higher allowable water content can reduce both capital and operating costs of dehydration equipment leading to improved economics for CCS projects.

A strategic combination of integrity software, relational databases, GIS, and GPS technologies reduced costs and increased quality of a comprehensive pipeline integrity assessment and repair program that Greenpipe Industries Ltd. completed recently on three crude oil pipelines—two 6-inch and one 8-inch—for Enbridge Pipelines (Saskatchewan) Inc. Greenpipe analyzed metal loss data from recent in-line inspection logs, calculated real-world coordinates of defects and reference welds, prioritized anomalies for repair taking environmental risks into account, and prepared detailed dig sheets and site maps using PipeCraft™, Greenpipe’s advanced GIS-based pipeline integrity-maintenance software package. GPS technology was used to navigate to dig sites and the accuracy of the GPS approach was compared with traditional chainage methods. Pipelines were purged and all defects were cut out and replaced by new pipe during a two-day shutdown on each pipeline. A comprehensive set of data, including high-accuracy GPS location of anomalies, reference welds, and replacement pipe welds, was collected at each dig site and entered into the PipeCraft relational database. After all repairs were completed, the client was provided with a GIS-based electronic final report, allowing point-and-click access to all data collected in the field, including in-line inspection logs, dig information sheets and as-built drawings. The new methodologies employed on this project resulted in a high quality, comprehensive and cost-effective integrity maintenance program.

At their advent, PDC bits were aimed at soft formation, fast drilling applications. However, as PDCs have come to dominate market share over roller cones, PDC bit development has shifted focus toward other goals such as durability and longevity which is often in conflict with high ROP. Returning focus to aggressive, high ROP drilling applications has required development of materials, design and manufacturing processes in alignment with that goal set. A cross-functional team was assembled to understand and focus on the high ROP concerns of the end customer and was tasked to develop a PDC bit platform aligned with these goals. This paper discusses general and application specific challenges posed by high ROP drilling applications and how they have been addressed by the aligned development of a new system of materials, design, and manufacturing processes used in PDC drill bits. Formation to bit interaction simulations and computational fluid dynamic modeling analysis are presented in support of the development hypotheses. Field results from case studies and broad field data analysis summarizing the results of extensive testing are presented as well. Driving ROP beyond the ceilings observed in many extreme ROP applications requires that energy be efficiently transferred not just to the bit, but focused on the cutters. To achieve this, an essential change to the base material of the bit body was made, exposing drastically new avenuesand hurdlesfor design and manufacturing. However, the simulation and field results presented confirm that the new system is able to consistently achieve the goal set in high ROP applications.