Risk Assessment Of Well Casing Structure Of Ultra-Deep Wells In Shunbei Area

Shunbei oil and gas field is a major oil and gas field discovered by Sinopec in recent years.This field’s geological conditions are complicated,including fractured zone,fault zone and fractured stratum,Frequent complex situations occur in the drilling process,which has become one of the key problems restricting the safe and efficient well construction in this oilfield.In order to fully understand the characteristics and distribution rules of the underground complex situations in this area,the reasonable casing program and measures to avoid drilling engineering risks are determined.Based on the data of logging,well history and drilling log of40 Wells in Shunbei area,this paper analyzes the characteristics of complex accidents and casing program in Shunbei area.Based on the collection of 40 Wells actual data such as well logging,mud logging,well history,drilling log,The reasearches about the analysis of complex accidents and well structure characteristics in Shunbei area,the establishment of formation three-pressure profile and safe drilling fluid density window,the risk assessment of drilling engineering,well structure optimization,the regionalization description of formation pressure in Shunbei area and the scheme of well structure have been carried out.The distribution characteristics of the complex conditions in different fault zones and the formation three pressure profiles which are predicted by logging data and corrected by real drilling data are obtained,the drilling engineering risk assessment method suitable for this area is established.Based on the regional formation pressure description and engineering risk assessment,a well structure recommenda-tion scheme suited for this area to avoid the complex situation is recommended.The results show that lost circulation,collapse and stuck pipe are common risks during drilling in this region,with lost circulation being the most serious risk type in this areas,accounting for 69% of the total risk types.Permian,Silurian and Ordovician are the formation with frequent loss of wells.The four open and five open casing program are the main ones in Shunbei area,and the key to prevent the occurrence of accidents is to seal the point strata.The combination of fracture pressure and the critical loss density of a particular formation can be used to create a loss pressure profile for the area,which can accurately predict the loss risk.Based on the generalized stress and strength interference theory,the risk assessment method of Shunbei areas was established,five Wells in Shunbei area were evaluated by this method,and the prediction accuracy reached 92.31%.Based on the common Kriging interpolation inversion after depth adjustment and horizontal correction,a regional description method of formation pressure in Shunbei area was established.The regional description of formation pressure shows that the pore pressure is higher in the north,especially in the northwest,and lower in the south of Shunbei area.The leakage pressure is lower in the north and higher in the south,and there is zero window phenomenon in the northwest.Based on the regionalized distribution of formation pressure,the analysis of the downhole complexity and well structure characteristics in this area,three characteristic regions of Shunbei area are pointed out: the north of No.a fault zone,the north of No.e fault zone and the junction of No.a fault zone and No.e fault zone.At the same time,according to the risk assessment results of the three zones,a series of well structure schemes for the three zones are recommended.