Fan Zifei

New Findings on Heatloss of Superheated Steam Transmitted Along the Wellbore and Heating Enhancement in Heavy Oil Reservoirs

At the conclusion of several cycles conventional saturated steam huff and puff in heavy oil reservoirs, the heating radius are typically only 20-30m as it went through successive saturated steam huff and puff. The heating scope can’t be enlarged by continuing saturated steam huff and puff any more. However, superheated steam huff and puff as a additional heavy oil recovery significantly increased heating radius of saturated steam huff and puff. Conventional saturated steam huff and puff theory is not applicable for superheated steam. In this study, superheat steam heat transmission mathematical models was established by three laws such as the law of conservation of mass, the theorem of momentum and the law of conservation of energy, thermodynamics and fluid flow theories. Based on models, the parameters such as temperature, dryness, pressure, degree of superheat, heat loss along the wellbore were calculated. This work analysis the superior properties of superheated steam and bring forward superiority of superheated steam huff and puff to effectively develop heavy oil reservoirs in recovery mechanisms, including simulation studies, and current pilot test effects.

Development and genetic mechanism of complex carbonate reservoir fractures: A case from the Zanarol Oilfield, Kazakhstan

Abstract By core observation and slice analysis, two types of fractures can be identified in reservoirs of Zanarol Oilfield, including macro-fractures and micro-fractures. Macro-fractures refer to tectonic fractures and stylolites, and micro-fractures mainly refer to grain breakage fractures and micro-tectonic fractures. The development of the different scale fractures is controlled by lithology, formation texture and stress field. Macro-fractures are well developed in tight rocks such as micrite and micro-fractures are well developed in granular carbonate rocks of good porosity and permeability. The Zanarol Oilfield is a typical layered pool, with interbeds of granular carbonates and tight carbonates, and this texture controls the vertical distribution of macro-fractures and micro-fractures. Macro-fractures in the ? layer are well developed due to its tight reservoir, and micro-fractures are well developed in the ? layer because of its loose reservoir. The planar distribution of the fractures is controlled by principal stress, and fractures are well developed in zones with high principal stress.

Oil property changes during the waterflooding for reservoirs with condensate gas cap

Abstract Zanarol Oilfield is a giant carbonate reservoir with condensate cap, weakly volatile oil, and bioclastic limestone of low porosity and permeability. During the waterflooding stage, formation pressure decreased step by step resulting from the former depleting development and the strong heterogeneity of carbonate reservoirs. The gas cap spread outwards with the formation pressure dropping, causing gas breakthrough in production wells near the oil and gas contact, GOR increased and oil density decreased. In the internal oil region far from the oil-gas contact, the dropping reservoir pressure led to dissolved gas separating out from oil, making crude oil change to black oil from weak volatile oil. With the separated solution gas, the oil density, produced gas oil ratio and oil viscosity increased, the oil well productivity decreased, all these make waterflooding more difficult. The main method for improving development response is to keep formation pressure and improve the utilization factor of water injection.

Major influencing factors of water flooding in abnormally high-pressure carbonate reservoir

The higher pressure coefficient is the major characteristics of the abnormal high pressure carbonate reservoirs, which the pressure coefficient generally exceeds 1.2 and the initial formation pressure is higher than normal sandstone reservoirs. Due to the large pressure difference between initial formation and saturated pressure, oil wells are capable to production with high flow rate by the natural energy at early production stage. When the formation pressure drops to the saturation pressure, the water or gas is usually injected to stabilize the well productivity and sustain the formation pressure. Based on the characteristics of Kenkiak oilfield, a typical abnormal high pressure carbonate reservoir, a well group model is designed to simulate and analyze the influence factors on water flooding. The conclusion is that permeability, interlayer difference and reserve abundance are the main three factors on the water flooding development in these reservoirs.

The research on influencing factors of new crack rediction for special low permeability reservior

The natural productivity of special low permeability reservoirs is low, which can not meet the industrial oil output standard, and the fracturing treatment must be carried out to take effective industrial development. There are many factors influencing the new crack redirection which carried out repeat fracturing. In order to research the change of stress field after repeat fracturing, the mathematical model of finite element method of two-dimensional stress field with considering the existence of fracture is established, and on that basis, combining with the actual oil field, the impact of stratigraphic principal stress difference, crack width, crack length and elastic parameter on the new crack is researched, which provide theoretical direction for reasonable arrangement of well pattern.