Workover activity

Wells are worked over to increase production, reduce operating cost or reinstate their technical integrity. In terms of economics alone (neglecting safety aspects) a workover can be justified if the net present value of the workover activity is positive (and assuming no other constraints exist). The appropriate discount rate is the company s cost of capital. 

Well production potential is the rate at which a well can produce with no external 

Normally acid would be allowed to soak for some time and then back-produced if possible along with the impairing products. One of the advantages of using coiled tubing is that it can be inserted against well head pressure so the well does not have to be killed a potentially damaging activity. 

When only small amounts of sand, wax or scale are experienced the situation can often be contained using wireline bailers and scrapers, run as part of a well maintenance programme. 

If water or gas breakthrough occurs (in an oil well) from a high permeability layer it can dominate production from other intervals. Problems such as this can sometimes be prevented by initially installing a selective completion string, but in single string 

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The industry is increasingly acknowledging the value of oontractors and service companies in improving their individual core capabilities through alliances, i.e. a joint venture for a particular project or a number of projects. A lead contractor e.g. a drilling company may form alliances with a number of sub contractors to be able to cover a wider spectrum of activities e.g. completions, workovers and well interventions. 

The capital cost estimates are generated by the Engineering function, often based on 50/50 estimates (equal probability of cost overrun and underrun). It is recommended that the operating expenditure is estimated based on the specific activities estimated during the field lifetime (e.g. number of workovers, number of replacement items, cost of forecast manpower requirements). In the absence of this detail it is common, though often inaccurate, to assume that the opex will be composed of two elements fixed opex and variable opex. 

Offshore oil production requires many chemicals for well drilling, for the treatment of the produced oil, for the treatment of gas, and for the stimulation and workover of the wells [100,101]. Altogether,25 classes of chemicals are used in offshore oil production [102]. The chemicals are undergoing increasingly detailed testing. As in other Quantitative Structure-Activity Relationships (QSAR), the octanol/water partition coefficient (Kq, ) is a crucial factor determining the environmental behavior and toxicity of the chemicals [103]. Toxicity... 

This term includes those employees engaged in activities related to drilling, well workover/completion/service, plugging and abandonment, maintenance, associated transportation, associated catering, and diving. 

It is important to determine the source of the biological problem. For example, gas-producing systems are normally free of biological activity. Contamination can arise from the introduction of bacteria with well-workover or completion fluids. Once established, such down-hole bacteria can continue to give problems. 

Surfactants or surface-active agents are chemicals that can favorably or unfavorably affect the flow of fluids near the wellbore and are, therefore, significant in considering well completion, workover, and well stimulation. 

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