Thousands of wireline conveyed perforating jobs are executed every month around the world; however certain jobs have a higher risk of weak-point breakage due to dynamic pressure loads, known as gunshock loads. Gunshock loads result from pressure waves in fluids and stress waves in structural components. Perforating under all conditions (i.e. static/dynamic overbalance or underbalance) can produce pressure waves and/or reservoir surge of large magnitude leading to wireline weak-point (WWP) failures and/or cable damage. These risks are assessed as part of the job preparations. In this paper we focused on Dynamic Underbalance (DUB) because perforating with DUB can deliver clean perforations with very low risk of gunshock damage when properly planned. For any perforating job on wireline, the magnitude and duration of pressure and stress waves depend on job parameters that can be adjusted, such as type and size of guns, shaped charges, gun loading layout, wellbore fluid, placement of packers and plugs, and cable size. For perforation damage removal we need a job design to generate a DUB of enough magnitude, using the right gun types and loading to produce a DUB of large-amplitude but short-duration, thus removing perforating rock damage while minimizing gunshock loads on the WWP. Perforating job designs are evaluated with software that predicts the transient fluid pressure waves in the wellbore and the associated structural loads on the cable and tools. All aspects of well perforating are modeled including gun filling, wellbore pressure waves, wellbore and reservoir fluid flow, and the dynamics of all relevant solid components like cable, shock absorbers, tools, and guns. When planning perforation jobs that may have a significant risk of weak-point breakage, we predict the peak dynamic loads on the cable and weak-point during the design process, and when necessary we make design modifications to reduce the peak load on the WWP. The software’s predictive capabilities are demonstrated by comparing downhole fast gauge pressure data (110,000 data points per sec), shock absorber deformation, and cable tension logs with the corresponding simulated values. Fast gauge pressure data from perforation jobs shows that the software predictions are sufficiently accurate to evaluate the gunstring dynamics and the associated peak tension load on the WWP as part of the job planning process. Residual deformation of shock absorbers correlate well with predicated peak axial loads at the WWP, and available cable tension logs from vertical wells show that the cable surface tension is well predicted. The simulation software described in this paper is used to minimize the risk of unexpected release of tools and guns due to perforating dynamic loads, thereby minimizing the probability of non-productive time (NPT) and fishing operations.

This paper presents one application of a simulation tool that predicts tubing-conveyed perforating gunshock loads reliably. The tool enables completion engineers to evaluate the sensitivity of gunshock loads to changes in gun type, charge type, shot density, tubing size and length, rathole length, use of shock absorbers, and placement of packers, among others.The simulation tool described in this paper helps engineers to identify perforating jobs that have a risk of gunshock related damage, such as bent tubing and unset packers. When predicted gunshock loads are large, changes to the perforating equipment or job execution parameters are sought to reduce gunshock loads and the associated risks.Comparisons between predicted wellbore pressure and actual fast-gauge pressure data are available in related SPE articles. These comparisons show that predicted wellbore pressure transients are very reliable both in magnitude and time. Peak sustained pressure amplitudes at the gauges are on average within 10% of software-simulated values. For cases where shock absorbers were used, residual deformations of crushable elements correlate well with the peak axial loads predicted by the software. The software is able to simulate perforating job designs in a short time, which allows engineers to optimize perforation jobs by reducing gunshock loads and equipment costs.The ability to predict and reduce gunshock-induced damage in perforating operations is very important because of the high value of typical wells. With the software tool described in this paper engineers can optimize perforation jobs by minimizing the risk of gunshock-related damage and the associated non-productive time (NPT).

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Summary Reservoir surveillance with pulsed-neutron-capture (PNC) logs has shown its importance historically in providing reservoir hydrocarbon saturations behind the casing. However, there is little in the literature to show the importance of PNC logs for contact tracking and accessing bypassed/moved hydrocarbons. In addition, no one has ever attempted to characterize the various borehole environments and subsequently understanding their impact on the PNC-derived hydrocarbon saturations. This paper is divided into two parts. The first part shows the importance of time-lapse PNC logs in understanding reservoir-fluid movement and chasing migrated hydrocarbons behind the casing. A case study from the UK Central North Sea is presented to highlight the importance of the PNC sigma data. The second part of the paper shows the computation of borehole-environment parameters from simple to complex completions including multiple casing/tubing strings, varying hole sizes, and annuli fill. For the first time, the work presented in this paper shows the importance of having correct environmental parameters and the impact of using incorrect parameters on the PNC-derived hydrocarbon saturations. Not making such detailed checks may result in misinterpretation of the PNC data, leading to incorrect conclusions about fluid dynamics, and risky decisions in adding perforations and water-shut off (WSO) opportunities.

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