Production rate and volume information are important for many reservoir surveillance and management tasks. For example, many techniques for estimating the remaining producible gas in a reservoir depend on accurately knowing the amount of gas produced from the reservoir in combination with the average reservoir pressure. History-matching gas, and water production data using a reservoir simulator is a common practice in workflows used for making investment decisions such as whether or not to drill more wells. The quality of a history-matched model is limited by the quality of the allocated production data. An additional need for quality rate allocation is that the production volumes for individual wells or reservoirs are often required for regulatory reporting.
Production allocation for high temperature and pressure is not easy task as the current orifice plate flow meter is not deigned for high condensate gas ratio (CGR). The error in using current meters could reach up to 60 percent in gas rate due to accumulation for condensate on the orifice plate. In this field, there are only two wells producing from two zones. There is only one production separator in the platform which makes the allocation difficult due to the need for shutting down one well to do multirate test on the other well. One of the wells has a downhole pressure gauge but the other well does not.
In this paper, we will present new procedures for using a combination of the downhole pressure and multirate tests to construct the accurate inflow performance curve (IPR) for each well. Then, at each reservoir pressure the relationship between wellhead flowing pressure and flow rate is programmed by Visual Basic program (VBA). This program is used to allocate daily gas rate from the wellhead flowing pressure.
This method shows high accuracy for allocating the history and current gas flow rate with high condensate ratio. Also, provide accurate well test analysis and accurate reserve calculation.
The availability of accurate production volumes, at the well level and throughout the production network, is fundamental to the workflows that target the optimization of the economic potential of the reservoir. Without an accurate understanding of production volumes, the company's field development and operational decisions may not support the maximum economic value of the reservoir and can undermine the accuracy of the reserves estimates1–2.
As mentioned there is only one production separator through which the Well-A & Well-B produced fluids entering for the first separation. Well-A starts to produce in September 2002. The problem started when Well-B was first introduced to the production in May 2005 and the flow meters now measured the total gas and condensate flow rates from both wells instead of one well which makes it difficult to allocate the metered flow rates back to the wells in an accurate method.
This problem generally affects the back production allocation for each well showing unreal well performance and inaccurate daily production monitoring and also affects the reserves calculation.