Abstract
The objective of this article is to demonstrate recent results of a water cut measurement campaign in the Karachaganak oil and gas condensate field. Historical, inaccurate well water cut assessment was due to the limitations of well test facilities which led to uncertainty in short- and long-term production forecasts. Several approaches were conducted to eliminate uncertainties in water cut measurements and to evaluate and define adequate tools to use for future water cut analysis.
The use of a mobile sampling flow loop installed at the well head, where turbulent multiphase flow is guaranteed, was a safe and reliable approach to measure the water cut of the producing low and high productivity wells. Sampling and analyzing the fluid at the well site at various operating well head pressures, frequently and for long periods of time, resulted in better understanding of water cut dependence with changes in drawdown. In addition to the use of sampling on site, the optical sensor (OS) technology was a trial tested on two wells along with the sampling flow loop to confirm the accuracy of the technology.
The existing test separators were not designed to handle high water rates; moreover, due to the complexity of the produced hydrocarbon, multiphase flowmeters are not able to accurately measure the correct fluid phase contribution and, as a result, inaccurately estimate phase rates.
The OS tool demonstrated accurate real-time water cut readings in the liquid phase, when compared with the flow loop samples, as long as a turbulent flow is guaranteed during measurement. Thus, this technology can be considered as an accurate tool for water cut measurements. The possibility of temporary and permanent installation of the optical sensor tool at the well site or test lines is under evaluation.
The current field development focuses on improved recovery from the oil rim which is above a weak aquifer. In the historically developed areas of the field this aquifer is separated from the hydrocarbons by impermeable shale and therefore water production has been minimal. Current and future development requires the drilling of new wells in areas not protected by barriers; this has led to a number of recent wells having a relatively early water breakthrough.
As a result of accurate water cut measurements, unallocated water in the field was well defined and led to better control of water producing wells to maintain stability of process facilities. This application confirmed the limitations and low level of accuracy of the existing well test separators.
The successful campaign to improve water cut assessment was critical to update and re-evaluate production wells’ operating philosophy, reservoir management, and the future development strategy of the carbonate reservoir.
