The SAGD pilot test in Liaohe oilfield of China is the first one conducted in the medium-deep extra heavy oil reservoir (650-800 m), using the combination of vertical injectors and horizontal producers. Temperature observation wells play the important role in the understanding of the pilot performance and optimization of the operation process. This paper will present the objectives, principle, interpretation and application of the temperature observation wells in the pilot area. The production problems were identified and solutions were sought to improve the SAGD performance, through the use of data obtained from the observation wells.
This paper is the continuation of CIPC paper 2006–146 presented in 2006. That paper introduced the successful test of the SAGD pilot in a medium-deep extra heavy oil reservoir in China[1]. The pilot has been expanded to include 12 horizontal wells since the presentation of the last paper two years ago. The earlier two wells have reached a daily oil rate of over 100 t/d per well. The current recovery factor is about 27% and the anticipated ultimate recovery is over 60%. Compared with the Canadian SAGD projects, the reservoirs in Liaohe oil field of PetroChina resulted in two difficulties using the SAGD technologies: (1.) reservoir depth exceeds 500 meters (530-810 m) compared to 200–500 meters in Canadian SAGD projects[2], the heat loss from the wellbore is relatively high and this increased the difficulty for injection and production facilities and (2.) the depletion by Cyclic Steam Stimulation (CSS) prior to SAGD application while majority of the Canadian SAGD projects are commenced in the original reservoir conditions. The current recovery factor by CSS in Liaohe is about 20%. Prior depletion by CSS complicates the conversion to SAGD applications and determination of operating parameters due to the altering in the distribution of the remaining oil saturation (Fig 1).
To overcome the difficulties associated with the SAGD applications in this reservoir, Lioahe Oilfield Company has taken various measures including the combination of vertical injectors and horizontal producers. The horizontal producers are placed in the lower part of the reservoir between two rows of vertical injectors to maximize the access of remaining oil saturations. A steam separator has been used to achieve high quality steam injection to maintain a quality of over 75% into the reservoir sand face (vertical depth of the reservoir is about 790 m); an over-sized tubing pump has been applied to provide the adequate lift capacity for the producers (peak liquid rate of 500 m3/d per well and the wellhead temperature of 180 °C).
The monitoring of reservoir temperature is most important for any thermal processes. The thermal couples are usually used in the thermal recovery process. However, it can not provide the continuous and on time measurements as required by SAGD temperature monitoring.
A distributed fiber optical temperature sensor system has been developed in recent years to provide the distributed, continuous and multiple functioned optical temperature measurement system.