VPLS/ MPLS is one of the most popular Wide Area Network (WAN) technologies used today by service providers. VPLS depends on pseudowires (PW) within Multiprotocol Label Switching (MPLS) network to emulate Ethernet connectivity in a full mesh topology, to multiple remote sites, sharing an Ethernet broadcast domain. As IP multicast services continue to be offered, many customers find it desirable to extend their multicast applications to remote sites, where traditional technologies fail to support such connectivity. A layer-2 VPN service using VPLS supports the extension of multicast services to remote sites. In this paper, the impact of a full mesh VPLS with the interoperability of Cisco Overlay Transport Virtualization (OTV) and multicast traffic has been analyzed. The paper concludes that an inadequately designed full mesh VPLS based WAN can have a significant negative impact on overall WAN performance in terms of reachability and packet loss for data, voice, and multicast traffic on the same customer edge (CE) device. The paper further proposes a design solution to avoid drastic impacts on the overall WAN performance when a large amount of multicast traffic is to be transported.
Well testing is very challenging especially in northern parts of Pakistan, as there are complex lithologies and multiple formations encountered in a single well. These formations include both fractured carbonates and sandstones. In addition, lower matrix porosities make it more difficult and time consuming as it can take several weeks to months to test multiple formations individually using a casedhole drillstem test (DST). These tests impact the overall well cost due to the extended rig time required and production loss. Extended buildups are a huge concern that must be kept in consideration due to the high rig-time requirement. This paper describes the application of a wireline formation tester (WFT) for interval pressure transient testing (IPTT), which is also referred to as a mini-DST, to estimate flow regimes and reservoir properties along with vertical pressure profiling, fluid identification, and sampling. This technique was applied at two of the exploratory wells in TAL block. There, WFT was deployed with a single probe and straddle packers to achieve the desired results across four potential reservoirs. Vertical pressure profiles across the prospective formations were acquired using the single probe; this was followed by a mini-DST using straddle packers to test zone by zone for fluid type, collect samples, and record pressure buildups. Real-time pressure derivatives were monitored to optimize the buildup time at each station depth. This integrated IPTT gave necessary reservoir information in a very short span of time. It saved significant amount of time and costs, especially rig costs and entire well testing cost giving valuable information for completion strategy.
Hydraulic or zonal isolation behind pipe plays a vital role in the life of a well. It guarantees well control, production from hydrocarbon zones and preventing the production of unwanted fluids. Perforation zone's selection and remedial jobs are based on cement integrity. Common challenges faced in cementing wells in Pakistan are presence of thief zones, water/gas invasion in cement and improper mud displacement resulting in cement channelling.Cement evaluation is as crucial as the cementing job itself. It is done using conventional sonic tools (CBL-VDL) which provides information about cement integrity. Sonic tools provide a qualitative uni-directional measurement. Then we have ultrasonic technology which measures "Acoustic Impedance" (AI) of annulus material; gives 100% azimuthal coverage with much better vertical and radial resolution than sonic tools. However, for light cements; the above conventional cement evaluation techniques cannot be used due to its limitations like:i) Effect of liquid and gas micro-annuli and dual casing ii) Inability to resolve micro-debonded/contaminated class G cement due to its threshold principle iii) Low acoustic impedance contrast between liquid and cement i.e. for liquid 1.4-2.6 MRayls and for light cement 1.5-3.6MRaylsTo address the above limitations a novel measurement of "Flexural Attenuation" (FA) is combined with AI that classifies the annulus material into three distinct states Solid, Liquid and Gas (SLG). In flexure mode casing is vibrated at an angle and combined with AI (vibration in thickness mode); giving us a unique output of SLG map. AI stand alone cannot evaluate light cements and contaminated class G cements with certainty.A case study is presented; where light cement slurry was used. FA and AI measurements technology was combined to evaluate for zonal isolation. First time in Pakistan an ICE "Integrated Cement Evaluation" processing was applied; specifically designed for light cements and confident answers were obtained successfully. The AI showed 40-50% liquid contamination whereas SLG map confirmed solidified light cement behind pipe. FA and AI together confirmed zonal isolation and in turn provided aid for successful well control and completion of the well.
Shale gas is a new horizon in Pakistan to meet growing energy demands. Comprehensive data gathering is mandatory for proper evaluation of a shale gas play and to determine feasibility of a prospect. Shale reservoirs require hydraulic fracturing to produce commercially. In Pakistan, stresses are normally high due to plate tectonics. In some cases, the lack of sufficient understanding of stress conditions has led to failures of full hydraulic fracturing operations. Stress testing is a technique used to evaluate formation breakdown pressures and minimum in-situ stresses. Stress profiles can be estimated using openhole log data, however direct in-situ measurement is needed for calibration. Wireline formation testers have been used in the field to measure formation pressures, estimate mobility and obtain good quality downhole samples. One of the advanced applications of the wireline formation testers is to measure insitu stresses in a wellbore to calibrate the mechanical earth model (MEM) and to design a feasible hydraulic fracturing job. Traditional wireline insitu-stress technique has been around for some time now, however the technique suffered from a limited pressure ratings, which was not enough to breakdown the formation. An advanced wireline formation tester module capable of achieving a break down through sleeve fracturing at a very high pressure was used for stress measurement for first time not only in Pakistan but worldwide. The technique involves setting a single packer module across the target shale zone and inflating the packer until the formation breaks down. Once formation break down is achieved, either a straddle packer is set across the target formation and injection is performed for fracture reopening, or another cycle is done with the single packer element to record sleeve reopening pressure. Detailed planning was done by the reservoir and geology departments. Four tests at four different locations were done in the target well where formation break down pressure, closure and fracture re opening pressures were estimated. This information is used for updating a 1D geomechanical earth model for the further use in planning full scale hydraulic fracturing treatment.
The objective of writing this success story is to demonstrate how technology, in particular low cost solutions, are key to economically sustain and secure production from mature fields. Tubing Patch technology has been successfully utilized in Pakistan for the first time to restore the well integrity and saved huge CAPEX by avoiding expensive rig workover. Tubing-Annulus pressure suddenly increased in one of water disposal well (WDW). Annulus pressure varied directly with variations in Injection rates which were the clear evidence that tubing-annulus communication had been established and basic check ascertains that well had integrity issue. Being the only injector in area all production and processing of gas is majorly dependent on its injection reliability and integrity. After detailed in-house working it was decided to run diagnostic logging with spinner (quantitative) & temperature log (qualitative) to identify the leakage points precisely. All potential leakage paths (packer, tubing, tool joints) were considered while selecting the diagnostic techniques to have conclusive results. Based on diagnostic logging three leakage points were identified. Before proceeding for remedial measures to restore the well integrity, it was mandatory to check health of old carbon steel tubing string therefore it was planned to acquire corrosion log. Based on corrosion logging results, completion tubular was established in good condition which steered to install tubing patches best Techno-Economical solution across the leaks to restore well integrity instead of rig workover for re-completion. Consequently, three tubing patches, were successfully applied using wireline in water disposal well and integrity of well was restored. C-Annulus was pressure tested even after six months of installation and no pressure drop was observed during this interval.
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