An Overview of South Pars Monobore Completions
South Pars Gas-Condensate Field and its southern extension, the North Dome, are located in Persian Gulf, which is separated by the international marine border. This field is the most giant known gas field in the world which is along the huge North east-South west trending Qatar-Fars Arch. Selecting the appropriate well completion design, equipment and installation techniques are frequent decisions required of oil and gas operators. Getting those decisions right typically leads to enhanced well productivity. In this present paper we would study the advantages and disadvantages of monobore completions used widely in this field.
More than one hundred development wells have been drilled in several development areas or phases of South Pars area so far which are in production now. Kangan Formation and Upper Dalan Member of Dehram Group collectively host South Pars Gas Reservoir. There are four main producing reservoir zones within this field, which from bottom to top are K4, K3, K2 and K1 and are separated by non-depositional surfaces or equivalent boundaries. monobore completion has used for this gas reservoir.
Monobore” describes a completion in which the ID of the completion string is the same size from top to bottom. The 7 inch monobore in South Pars has two runs for completing the well. The first run is setting the packer on top of lower PBR, and a second run to tie back seal with tubing and 3SV. As the industry moves toward high rate gas completions, many of which will rely on 7-in. tubing, the benefits of running monobore completions are more readily attained. These benefits fall into two main categories: 1-well production 2-remedial operations.
Advantages of running monobore completion in South Pars
The most obvious benefit associated with increased tubing size is greater per well deliverability.
This reduces the number of wellbores required to drain a reservoir efficiently. For offshore projects in particular, this can mean a reduction in the number of platforms required. Reducing the number of wellbores decreases both operational and maintenance expenses for the field. Long-term reliability is increased as monobore completions tend to be less complex than standard completions and the elimination of internal restrictions reduces areas of gas turbulence. To demonstrate the well production benefits, a hypothetical high-rate gas reservoir was constructed from which inflow performance models.
The remedial advantages of monobores may not be realized until later in the field’s life. Running service and intervention equipment is made easier by the elimination of restrictions. In addition, one has full access to the liner top to allow easier squeeze or mechanical isolation. By increasing tubing size, thus reducing the frictional pressure drop during production, it is possible to delay the need to bring compression on line as well. Thus, the value of increasing tubing size can reach into the millions of dollars for infrastructure, wellbore construction and maintenance alone. However, the dramatically decreased field development times that running 7- in. monobores provides cannot be ignored. This shortened time to first production will allow operators to either Produce first gas much quicker or delay starting the project by that same amount of time. This factor can be the most significant impact on the net present value of a large project. For many projects, this increase in value pays for the increase in cost associated with using larger tubing.
Static seal on tie back seals helps to reduce potential for damaged seals by restricting of movement. Doing so has several advantages. First, the completion will be less complicated and a potential leak path is eliminated.
To realize these benefits, a packer capable of withstanding all compressive and tensile loads on the tubing string during production, stimulation or well control operations if needed.
Disadvantages of running monobore completion in South Pars
There are two disadvantages that associated with this system. First is difficulty of testing the packer. If liner top packer already had integrated, after setting the top packer then no test can be performed to confirm that the packer has fully set and provides full barrier and the second disadvantage is that the packer is not retrievable.
Natural gas is becoming a larger portion of many nations’ energy strategy. Thus, the pressure to deliver gas supplies safely, reliably, and more economically is growing. The benefits associated with monobore completions in general, and large monobore completions in particular, will help realize this goal despite its disadvantages it has been the best choice for this reservoir.
Pooya Alizadeh and Vahid Daneshkhah