The influence of barrier coastal sedimentary system lost circulation in sandstone

Abstract Sandstone formed in the barrier coastal sedimentary system is conducive to forming a good reservoir, which has great development potential. However, severe lost circulation occurs during drilling and cementing occasionally due to its complicated lithology. It is of great significance for safe and efficient drilling to understand this pattern of lost circulation accurately. The characteristics of vertical complicated lithology and regularities of the distribution of leakage zones are less considered in the existing method and model. Therefore, they cannot guide for field practice due to the huge difference from reality. In this paper, a new method combining geology and engineering is proposed to analyze the lost circulation pattern of sandstone formed in the barrier coastal sedimentary system. Stratigraphic characteristics and types of leakage zones are classified by logging data combined with sedimentary sequence analysis, and then the physical and geometric model of the single well in heterogeneous formations is established. The mathematical model is established using the discrete fracture-matrix coupling method and solved by the finite element method. According to the calculation results, the pattern of lost circulation in sandstone is studied, and the main factors affecting the lost circulation are analyzed. The results show that the barrier coastal sedimentary system mode influences the characteristics of lithology and the development type of leakage zones. The continuity of the sand body and fractures development significantly influence the characteristics of lost circulation. Fracture width and drilling fluid density have significant effects on the shape of the mud loss curve while drilling fluid viscosity and rate of penetration have little effects on it. For the complicated lithology, the superposition of different small layer mud loss curves can reflect the real lost circulation more accurately, which can provide a reference for the selection of lost circulation prevention and sealing measures.