ADVERTISEMENT

Managed-Pressure Drilling Used Successfully for Offshore HP/HT Exploration Wells

The South China YQ Basin, with its 15 trillion m3 of natural gas, is typical of ultrahigh-pressure/high-temperature (ultra-HP/HT) plays, with the highest bottomhole temperature (BHT) at 249°C, the maximum bottomhole pressure (BHP) at 142 MPa, and an extremely narrow pressure window. Predictably, drilling challenges in these plays are numerous. This paper discusses the successful application of managed-pressure drilling (MPD) in the basin with reduction in risks and well costs.

Overview of the YQ Basin

In recent years, approximately 27% of major oil and gas discoveries have come from HP/HT fields. The South China YQ Basin is one of the three major offshore HP/HT regions in the world and is located at the intersection of the Eurasian, Pacific, and Indo-­Australian plates and has a complex geological structure.

The drilling in this basin, as is the case in any HP/HT area, faces various technical challenges, including the following:

  • The temperature and pressure gradient is very high. The highest temperature gradient is 5.51°C/100 m. The formation-pressure transition zone is short, and the formation pressure rises rapidly.
  • The safety drilling-fluid-density window between pore pressure and fracture pressure is extremely narrow, and the safety factor is very small.
  • Formation pressure is hard to predict accurately, and the associated error is greater than 20% in some complex wells.
  • Formation drillability is bad because the main targeted layer is over 5000 m. As a result, the rate of penetration (ROP) is very low, which leads to longer drilling cycles and more-frequent downhole accidents and issues such as casing wear.
  • The natural environment is harsh (i.e., frequent typhoons in summer).
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191060, “Operational Design and Application of MPD in Offshore Ultra-HP/HT Exploration Wells,” by Qishuai Yin and Jin Yang, China University of Petroleum; Bo Zhou, CNPC; Ming Luo, Wentuo Li, and Yi Huang, CNOOC; and Ting Sun, Xinxin Hou, Xiaodong Wu, and Junxiang Wang, China University of Petroleum, prepared for the 2018 IADC/SPE Asia Pacific Drilling Technology Conference, Bangkok, 27–29 August. The paper has not been peer reviewed.
...
This article is reserved for SPE members and JPT subscribers.
If you would like to continue reading,
please Sign In, JOIN SPE or Subscribe to JPT

Managed-Pressure Drilling Used Successfully for Offshore HP/HT Exploration Wells

01 March 2019

Volume: 71 | Issue: 3

ADVERTISEMENT


STAY CONNECTED

Don't miss out on the latest technology delivered to your email weekly.  Sign up for the JPT newsletter.  If you are not logged in, you will receive a confirmation email that you will need to click on to confirm you want to receive the newsletter.

 

ADVERTISEMENT

ADVERTISEMENT

ADVERTISEMENT

ADVERTISEMENT