Two fields are of Hai Thach and Moc Tinh of the Block 5.2 and Block 5.3 in offshore Vietnam have been discovered and exploited of the oil and gas production since the middle 90s. At this time, many contractors will be drilled wells development in the fields with 16 wells by using Tender Assist Drilling (TAD). There are high-temperature, high-pressure (HPHT) in the two fields with the bottom hole temperature range from 140 °C to 175 °C and the bottom hole pressure range from 10,000 psi to 11,500 psi. Through drilling and construction wells have been met many problems related to high pressure high temperature wells. Especially in the discovery well and appraisal wells in high pressure, high temperature reservoir (HPHT), There are a lot of incidents and operating technical problems during drilling. One of the problems during drilling is the gas influx into the wellbore due to the abnormal pore pressure, shallow gas, fluid loss due to the fracture pressure and pore pressure is very narrow margin, stuck down hole equipment in the wellbore due to high differential pressure between hydrostatic pressure and pore pressure and another problem was related to drilling mud and cement. At the stage of wells developemnt, the biggest challenges deal with design HPHT wells, which are required to high efficiency during drilling, construction wells and also require to bottom hole assembly working for a long time and a safe in the reservoir condition of high-pressure, high-temperature. Although the principal design HPHT wells was not different to principal conventional wells, but that well was still potentially risky and very challenging because of the strict design HPHT wells have not much been to choice materials and equipment. This study has been presented in detail the difficulties, solutions, and the effect of high –pressure, high-temperature on wells design development in HPHT conditions such as Casing design and selection grade, the differential pressure between reservoir pressure and fracture pressure is a narrow equivalent circulating density (ECD) management, laboratory the effect of temperature on rheological properties and model behavior of drilling fluid by using V35 fann, selection drilling mud in drilling wells HPHT conditions. Also techniques have been shown the lesson learned to drill and construct wells in high pressure, high temperature condition in offshore Viet Nam.

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