No abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFactors and mechanisms leading to sanding are described within an integrated rock and soil mechanics framework. While the conventional sanding models generally consider a single-mechanism for sanding, namely the critical depletion resulting in rock disaggregation, the proposed approach considers the inter-play of several mechanisms that can lead to the rock break-up and sand transport. One important difference is that rock disaggregation is not seen to represent the onset of sanding as the sand mass can offer significant resistance due to frictional properties, interlocking of sand grains and arching. The approach presented can be used to explain why sanding in the field tends to be episodic and how depletion, which is a major factor in rock break-up, can be highly effective in holding broken up sand grains together and become a sand stabilization agent.The proposed approach is used in discussing sanding at several wells in two different fields. These wells have been in production for several years and show that sanding cannot be linked to just one unique mechanism (e.g., depletion). However, once all mechanisms for sanding are incorporated, a more consistent analysis can be used by completion and production engineers to make more objective and pragmatic decisions in managing sanding while maximizing production over the life of the well.

Summary Surveillance data can be critically important in managing producing oil and gas fields. To maximize value, it is necessary to identify those surveillance opportunities that are not only informative, but materially value-adding. For surveillance decisions in producing fields, applying conventional value-of-information (VoI) methods to every individual surveillance opportunity can be too time-consuming to be practical, considering the large number of relatively small data decisions to be evaluated, each possibly addressing multiple reservoir uncertainties and supporting numerous business decisions. This paper outlines risk-based surveillance planning (RBSP), a simple approach that is based on the observation that the vast majority of surveillance opportunities in producing fields are designed to manage risks. RBSP then evaluates surveillance opportunities with VoI principles, but exploits the fact that much relevant value data already exist as byproducts of risk-management processes. RBSP has been used successfully in dozens of oil and gas fields; two case studies are described herein. Many companies use a risk-management framework that documents risk events and their causes and consequences, assesses risk probability and impact, and identifies prevention measures to reduce the probability of the risk events occurring and mitigation measures to reduce the impact of risk events should they occur. If such a framework has been used, the risk assessment provides an estimate of the expected monetary value (EMV) lost because of a risk event (= probability × impact). Risk reassessment taking into account the planned prevention and mitigation measures reveals the EMV increment attributable to the risk-management measures. RBSP assumes this to be the theoretical value of “perfect” information (VoIperfect) for the package of surveillance that supports these measures. RBSP links each potential surveillance opportunity to the risk-management plan by determining how the surveillance would (a) help create or strengthen prevention measures; (b) detect the impending occurrence of a risk event, thus enabling mitigation measures to be triggered; or (c) help monitor both prevention and mitigation measures to detect any weaknesses that require improvement. The VoIperfect of a surveillance opportunity with respect to a given risk can then be estimated by attributing to it a proportion of the total VoIperfect of the surveillance package by use of a simple criticality score to estimate how dependent the risk-management measures are on each item of surveillance. A reliability score then discounts this VoIperfect on the basis of how likely the surveillance is to deliver the necessary information in reality, yielding the value of imperfect information. Where an item of surveillance affects several risk-management measures and multiple risks, the values are summed, providing a VoI for each item of surveillance. In case studies of an asphaltene-precipitation risk in a deepwater oil field and a water-influx risk in an offshore gas field, RBSP helped to create a logical value-based rationale for surveillance decisions, and the surveillance, when implemented, did facilitate effective management of the risks and added value.

Factors and mechanisms leading to sanding are described within an integrated-rock and soil-mechanics framework. While the conventional sanding models generally consider a single mechanism for sanding, namely the critical depletion resulting in rock disaggregation, the proposed approach considers the interplay of several mechanisms that can lead to the rock breakup and sand transport. One important difference is that rock disaggregation is not seen to represent the onset of sanding, because the sand mass can offer significant resistance from frictional properties, interlocking of sand grains, and arching. The approach presented here can be used to explain why sanding in the field tends to be episodic, and how depletion, which is a major factor in rock breakup, can be highly effective in holding broken-up sand grains together and, in fact, become a sand-stabilizing agent.The proposed approach is used in discussing sanding at several wells in two different fields. These wells have been in production for several years and show that sanding cannot be linked to just one unique mechanism (e.g., depletion). However, once all mechanisms for sanding are incorporated, a more consistent analysis can be used by completion and production engineers to make more objective and pragmatic decisions in managing sanding while maximizing production over the life of the well.

The reservoir is our primary asset - "surveillance is the maintenance strategy to enable delivery"–You would not dream of poor maintenance delivery on plant and well integrity–How do we minimize poor maintenance of reservoir delivery? Surveillance is our primary tool for managing reservoir and well delivery; however, it is not always properly thought through and executed. On occasions we fail to act on the data we have, or capture lessons learned. Acting on this information is often where we stumble. Our ability to follow a plan, do, measure, learn loop is key to good execution and delivery of a surveillance programme that delivers the short term production and long term reserves recovery. Introduction Surveillance is a key component of our operations, no matter what stage that we are at in our field life cycle, but it is still an area that is under threat when we prioritise our work programmes and expenditure. In today's world it is absolutely essential that we recognise the importance of "hard" data such as basic production and injection volumes or data that we cannot go back for, such as PVT. It is also important to establish trends in data acquisition, as this provides a clear way into understanding changing reservoir performance over time e.g. changing OWC/GWC or saturations through field life. In a modern world however, it is the challenge of operating in a real tme world, which will provide us with increasing opportunities to understand what is happening now and being able to act on this through new technology and processes of working. Our challenge is to embrace both the traditional and the new surveillance technologies of today and make them deliver significantly more than we have in the past. Surveillance Planning Whether we are operating a new or mature field, developing a fully integrated surveillance plan is essential. A focussed surveillance plan must have:–a clear view of the risks, uncertainties and opportunities which face us in our reservoir depletion/management plan–a well integrated team, with a key surveillance single point of accountability to develop the plan. Surveillance planning can however be progressed by linking to two common objectives, managing base production and the identification of new opportunities. This ensures that we have delivery of surveillance in the short, medium and long term. We are as an industry very good at delivering the here and now, but I would question our ability to consistently deliver the long term surveillance, which is an essential component or our reserves delivery and non proven resource progression. Our planning philosophy follows a simple common step wise approach to surveillance associated with base management, new wells delivery and resource (non-proved) progression.