Quasi-continuous hydrocarbon accumulation: An alternative model for the formation of large tight oil and gas accumulations

Abstract

It has been revealed that the formation of most giant tight oil and gas fields is inconsistent with both the typical basin-centered/continuous hydrocarbon accumulation (CHA) model and the discontinuous hydrocarbon accumulation (DHA) model. We argued that hydrocarbon accumulations in tight reservoirs are dominated by an intermediate form between these two models, termed quasi-continuous hydrocarbon accumulation (QHA). This accumulation model is akin to the CHA in that both are extensively distributed with no distinct boundaries. However, oil and gas in the CHA occur within source rocks, accumulate mainly at or nearby where they are generated, have undergone no significant migration, and their occurrence is not controlled by traps. The QHA, however, occurs in tight reservoirs in the vicinity of source rocks. The accumulation of oil and gas occurs in multiple closely related lenticular or blanket-like reservoirs that are laterally adjacent and vertically stacked. Neither noticeable inversion of oil/gas and water nor complete bottom water or edge water is present. The charging of hydrocarbons is pervasive and the migration is mainly driven by overpressures, while the effects of buoyancy are limited. Hydrocarbon accumulation is not controlled by anticlinal traps but mainly governed by non-anticlinal traps. In fact, the CHA and DHA represent two end-member types of hydrocarbon accumulation and the QHA is a transitional mechanism by which most giant tight oil and gas fields are formed.