Challenges in Determination of Water Content and Condensed Water in a Multistacked Sour Gas Field Containing High CO2 Content Offshore Malaysia
Authors: Wong Tiong Hui , Masoudi Rahim , Philpot Jared Anthony , Othman Mohamad 
Published: March 2015

The amount of condensed water should be carefully estimated in gas development plans, especially for fields with high CO2 content. This may affect the design of the well, surface facilities such as water treatment equipment and CO2 removal units, and flow assurance and corrosion control strategies. However, reliable prediction of the water content of gas with high CO2 level in contact with formation brine is still a challenge.

The actual condensed water production data from a sour gas field offshore peninsular Malaysia has indicated that the condensed water levels are higher than estimated in the field development plan (FDP). The trend of water/gas ratios (WGR) across the field was analyzed versus depth, pressure, temperature and CO2 content of the reservoirs. To isolate the primary source of errors in the measured WGR from production tests, the measured water/condensate splits were verified with liquid/gas ratio (LGR) using calculated CGRs based on equation-of-state models. Salinity measurements of lower than 300 ppm were considered as fresh water. Equilibrium-based predictive tools were used to estimate the condensed water levels according to gas composition, pressure, temperature and water salinity. The results demonstrate significant differences between the EOS model prediction and the actual condensed water production. This might be due to the CO2 content of different reservoirs, in-situ pressure-temperature conditions, formation water salinity, the water vaporization around the wellbore due to the high gas velocity, the dry-out effect, or may be attributed to non-equilibrium concepts.

This paper details the investigation of high condensed water production in the field and what cautions that must be taken into account in developing such fields. A new correlation was developed to predict the amount and trend of condensed water in the field with various CO2 levels. The study results can be used as a useful reference during the development planning of similar fields.

Introduction

The amount of water production from the gas fields prior to water breakthrough can be affected by both thermodynamic and kinetic bahaviour of the fluid flow in the reservoir and more particularly in the near wellbore area. Parameters, which affect the thermodynamic conditions and determine the water content of the gas, are temperature, pressure, formation water salinity, gas composition and CO2 content. Near wellbore area kinetic and non-equilibrium facts such as gas velocity, drawdown, gas stripping, water vaporization and dry out phenomena may also affect the amount of the produced water. All of these parameters must be considered to quantify the produced water prior the water breakrough time.

During full field review of a particular sour gas field on the edge of the Malay Basin, it is observed that at the initial stage of reservoir life, many of the field's reservoirs were produced with constant higher water levels than the estimated condensed water based on the equilibrium conditions. Investigation has been undertaken to explain the source and amount of high water production in the field. The high condensed water levels should be considered carefully in the development plans for high CO2 levels gas fields in the region as they may impact the design of surface facilities, such as water treatment equipment, CO2 removal units and corrosion protection for pipelines.