Abstract
The objectives of the paper are to present well start-up (SU) challenges that Tengizchevroil (TCO) experienced operating at high pressure gathering system in the last 3-5 years and to discuss the established strategies that were used to overcome these challenges to optimize production on daily basis. Additionally, the paper reviews the production strategies that were used to efficiently manage relatively low-rate wells that were produced in a cycling fashion due to loading tendencies.
Well SU recommendations are generally prepared by carefully considering several key factors, such as static reservoir pressure, flowline (FL) volume, gathering system back pressure, and wellbore fluid gradient. By analyzing historical SU attempts of differently conditioned wells, specific thresholds or minimum requirements were established in connection with abovementioned factors. Each of these factors can be improved to maximize a well’s SU chance; for example, a smaller FL volume can be artificially increased at meter station (MS) side, or its FL pressure (back pressure) might be lowered. Furthermore, if there is still a low confidence on a particular well SU, a nitrogen injection can be performed to decrease fluid gradient in wellbore and subsequently maximize a well’s SU chance. Finally, other key nuances impacting well unloading were also considered, such as choke opening strategy to prevent choke plugging and reduction of MS pressure for a short time to ensure a full well SU.
TCO managed to efficient SU more than 300 wells on annual basis in last 3-5 years without any safety incidents. Each SU attempt was carefully reviewed and did not proceed until potential wellsite risks had not been mitigated to an acceptable level. With the established strategies, more than 85-90% of all SU attempts had been successful, and wells were returned into production after scheduled shutdown (SD) activities. Poorly planned SD activities might easily cause unnecessary and repetitive SU attempts and subsequently unplanned well downtimes. Such situations might cause up to $100,000-$500,000 production impact due to unavailability of surplus production from field at certain times in addition to unnecessary potential safety risks and extra greenhouse gas emissions emitted from repetitive SU attempts.
This paper summaries challenges, best practices, lessons learnt, some established planning strategies and well loading prediction strategies that are used to optimize and efficiently manage more than 150 producing well stock before TCO will fully switch to low pressure gathering system. The described well SU strategies can be used in other fields and prevent potential LPOs (Loss of Production) at certain situations.
