Discovery of “Enveloping Surface of Oil and Gas Overpressure Migration” in the Songliao Basin and its bearings on hydrocarbon migration and accumulation mechanisms

The Fuyang oil layer of the Songliao Basin is a tight and low-permeability sandstone pay zone formed in the fluvial-shallow water delta environment.In the formation are mainly lithologic reservoir and tight reservoir.The lacustrine-mudstone of K2qn1 is a good source rock and also acts as a good regional cap rock.The Fuyang oil layer is a typical upper-source and lower-reservoir pattern distributed in a large area.Based on a large number of exploration and development data, a macroscopic enveloping surface is found developed in the Fuyang oil layer, which is below K2qn1.The effective reservoirs within the enveloping surface are commonly saturated with oil, and below the enveloping surface are mainly water layers.The distance from the enveloping surface to the bottom of the source rock is usually 100-350 m and at most 550 m.Through the research of the distribution patterns and the physical properties of the sandbodies above or beneath the source rock, it is concluded that: 1) the enveloping surface is the boundary of the overpressure hydrocarbon migration; 2) the spacial distribution of the pressure release beds controls the direction and the distance of the overpressure hydrocarbon migration; 3) tight oil reservoirs and lenticular oil reservoirs are mainly formed inside the envelope surface, whereas, conventional reservoirs are formed outside the envelope surface as a result of the buoyancy hydrocarbon migration.The discovery of the "overpressure hydrocarbon migration enveloping surface" and the concepts of overpressure hydrocarbon migration and buoyancy hydrocarbon migration not only challenge the old notion that "hydrocarbon migrates along the faults and is distributed along fault belts" in the Fuyang oil layer of the Songliao Basin, give a new explanation to the long-distance-oil-downwards migration (hundreds of meters) and expand the exploration potential of the Fuyang oil layer, and provide a rational guidance to the exploration of syncline plays, but also better categorize tight oil/gas and conventional reservoirs in all of the key elements related to hydrocarbon migration, accumulation, reservoir characteristics and oil and gas spatial distribution.

Analytical modeling of geometric errors induced by cutter runout and tool path optimization for five-axis flank machining

The cutter runout effect has significant influence on the shape of cutter swept surface and the machining surface quality. Hence,it is necessary to integrate the cutter runout effect in cutter swept surface modeling,geometric error prediction and tool path optimization for five-axis flank machining. In this paper,an envelope surface model considering cutter runout effect is first established,and geometric errors induced by runout effect are derived based on the relative motion analysis between the cutter and part in machining. In the model,the cutter runout is defined by four parameters,including inclination angle,location angle,offset value and the length of cutter axis. Then the runout parameters are integrated into the rotation surface of each cutting edge that is used to form the final cutter envelope surface for the five-axis machining process. Thus,the final resulting geometric errors of the machined surface induced by cutter runout can be obtained through computing the deviations from the nominal cutter swept surface. To reduce these errors,an iterative least square method is used to optimize the tool paths for five-axis flank machining. Finally,a validation example is given for a specific ruled surface. Results show the effectiveness and feasibility of the analytical model of geometric errors induced by cutter runout,and also show that the geometric errors can be reduced significantly using the proposed tool path planning method.