Completion Robustness as a Production Management Tool: Case History in a Mature Offshore Field

Abstract

There is an ever present demand for increasing or maintaining the oil and gas production, on a production unit basis. Thus, it is very important to have a method to define the maximum safe production rate from the completion point of view. In recent years some oil companies introduced sophisticated integrated asset models for production optimization which include well quality assessment and surveillance. This approach allows a quasi-real time production optimization. This paper introduces the concept of completion robustness, related to the maximum safe production rate, and applies it in a low level of well surveillance floating production unit. Some relevant aspects of the production unit regarding the wells are: subsea completions, a broad range of sand exclusion systems, and most of the wells are on stream for seven years. The paper presents the completion robustness concept, the general method to apply it, and the procedures developed for the specific case study, in which the connectivity between the formation and the well through the sand exclusion system plays an important role. The main product attained is a list ranking the wells in terms of completion robustness. Based on this list the asset team can decide which wells may support a production increase, which wells must be kept in the current status, and which wells need an intervention or a rate reduction. The main conclusions achieved are: the completion robustness concept is a rational approach to define maximum safe production rate per well from the completion point of view; the method and procedures developed, although suitable for production units with high level of reservoir and well key parameters surveillance, can also be applied to low level of surveillance ones; the use of the completion robustness by the production operations teams have the potential to increase the production output and the wells longevity. Introduction Many developing projects offshore Brazil demands fewer wells per project for economics reasons. Designing high-rates offshore wells for maximum safe production rate (MSPR) is a challenge. In Campos basin a large number of wells completed with sand exclusion systems (sand control wells) are on stream for seven years or more. Establish the MSPR for these wells, considering various degrees of degradation, is also a big challenge. This study introduces the concept of completion robustness (CR), which is related to MSPR, and applies it in a case study on sand control wells hosted in a production unit with low level of reservoir and well parameters surveillance. In Campos basin over 150 inside casing gravel packs (GP), above 150frac packs (FP), and more than 250 horizontal openhole gravel packs (OHGP) and a few cases of stand alone screens (SAS) have been installed to date (Neumann et al. 2002; Marques et al. 2007). Despite this significant number of sand control wells it was not possible to find a criterion, better than a drawdown limit, to define MSPR based on these wells analyses. The main reasons for that are:there were relatively few sand exclusion systems failures in Campos basin;most of the failures were "infant" failures or late life failures after repeated treatments for damage removal;there are a large number of intervenient variables;a few successful wells may have never required gravel pack installation;strong cyclic loads, such as water hammer, are difficult to track;some missing data caused by poor reports and several information system changes along the time. Tiffin et al. (2003) presented a method for determining MSPR based on analysis of over 200 sand control wells. Their analysis indicated that screen erosion was certainly the most frequent failure mechanism for cased hole frac-pack and gravel pack. They introduced a criterion based on an erosion factor for determining MSPR for these completions and maintained the drawdown limit for OHGP completion. The erosion factor is the product of the square root of fluid mixture density and the flow velocity exiting the perforation tunnel, vc. Their results showed that for gas well the start of high failure rate occurred for vc around 20 ft/sec, while this value is about 10 ft/sec for oil wells.