Abstract:

By analyzing cores,thin section and pressure build-up tests,this paper discusses the occurrence of natural fractures in the reservoirs.The earth stress characteristics are identified through research on Kayser effect,seismic anisotropy,paleomagnetic and borehole cave-in.The direction of maximum horizontal major stress is perpendicular or near perpendicular to the direction of the major faults and natural fractures,while is in parallel with the direction of artificial fractures.The direction,length and strength of natural fractures are quantitatively predicted through the methodology of main curvature.The natural fractures are predominantly of tectonic origin and were mainly formed during the deposition of the Tertiary Dongying Formation.During different stages of development,natural and artificial fractures have different degrees of influences on waterflooding.Given the natural fractures being basically closed,attentions should be focused on the artificial fractures when designing injection-production pattern.

Key words: low-permeability reservoir, earth stress, natural fracture, artificial fracture, water-injection, Wendong oilfield