Understanding the Deviation of Horizontal Wolfcamp Well GOR from Type-Curve GOR in the Gas-Condensate Region of the Permian Basin

摘要

The objective of this work is to explain the deviation in GOR/GLR (Gas-Oil-Ratio/Gas-Liquid-Ratio) of hydraulically fractured Wolfcamp horizontal shale well(s) from the type-curve GOR/GLR in the gascondensate region of the Permian Basin. We relied on the detailed field data reported during the flow-back period of a recently completed well. We identified various aspects of the casing-tubing design, operational changes that were made and any concurrent production disturbance that were noticed. Then we did a thorough literature review of GOR/ GLR behavior in gas condensate wells. We identified the key concepts that were applicable to the well in our study. We applied the existing equations for the critical gas rate required to lift liquids in gas wells and highlighted the variation in gas velocity with changing pressure and temperature along the vertical part of the wellbore. Using this approach, we demonstrated the relationship between changing liquid fraction along the vertical part of the wellbore with the changing gas velocity. A wide range of GOR/GLR was noticed for the well in our study over a period of only a few days of flow- back. The GOR/GLR curves from the nearby producing wolfcamp wells and the PVT diagram available from a nearby wolfcamp well could not explain the observed deviations in GOR/GLR. However, there were some key changes made in the production methodology during the flow-back period. We identified the appropriate mechanisms of multi-phase flow applicable to each operational change during flow back. After identifying the appropriate multi-phase flow back mechanism, we implemented the concept of critical gas velocity (flow-rate) along the wellbore. This enabled us in explaining the GOR/GLRs observed in each operational regime. The corrected GOR/GLR of the well in study aligned with the GOR/GLR of the type- curve of horizontal shale wells obtained from the nearby hydraulically fractured horizontal wells targeting the Wolfcamp in the same formation. This is a unique study that utilizes the concept of critical flow rate, the different mechanisms of multiphase flow in the production tubing and annulus in identifying the advent of liquid loading. This work assists in explaining the discrepancies observed in the GOR/GLRs in the early production history of horizontal gas wells in gas-condensate regions. In the past, the concept of liquid-loading and the proposed remedies have been applied late in the life of gas wells with small gas rates to explain the abnormaility of the the GOR/GLR. This paper shows that the observed GOR/GLRs on the surface is not solely a function of the PVT diagram. Finally, integrating the learnings from this well with the liquid-loading concepts, we make recommendations for improved completions and flow back methodology for future wolfcamp horizontal gas-condensate wells in the Permian Basin.