Abstract
Petrom operates offshore oil and gas fields on the continental shelf in the Black Sea in Romania. These mature fields were discovered in the late 1970s and early 1980s in sandstone reservoirs with average well depths of 5500ft to 7200 ft (1700m to 2200m). Until recently, production has been with both free flow and gas lift. Over the past three years, ESPs have been installed in five wells resulting in production increases. The paper reviews the ESP completion designs and focuses on the impact of real-time data on the run lives and uptimes achieved over the past 3 years. To analyze the well performance, a new technique based on the ESP torque equilibrium equation between the pump and motor was utilized to reconstruct a continuous rate versus time profile using real-time data. This provided greater resolution in rate measurement than that provided by traditional surface well testing, which proved instrumental in understanding the ESP behavior in these wells which exhibited low flowrates (typically less than 100 Sm3/d, i.e., 600 bbl/d) and high GORs. The authors explain how the technique is valid in both transient and steady state conditions and therefore calculates the instantaneous flowrate at any time when real-time data are available. This continuous "rate log" as opposed to episodic rate data from well testing enabled superposition technique to be used to monitor drainage area average reservoir pressure, to confirm the relationship between motor temperature and well rate, and to observe the effect of high GVF (Gas Void Fraction) through the ESP. In the future this methodology can be used for back allocation and a reduction in surface well testing. In addition to the interpretation of rate data, there are important lessons learnt on how to achieve high ESP uptimes in excess of 98% using real-time data alarms.
