Geochemistry and origin of Ordovician oils in the Rewapu Block of the Halahatang Oilfield(NW China)

The oils in the Rewapu Block of the Halahatang Oilfield in the Tarim Basin(northwestern China) were geochemically analyzed by gas chromatography–mass spectrometry to investigate their origin and possible secondary alteration. The physical properties and chemical compositions of these Ordovician oils vary greatly, ranging from light to extremely heavy oils. All these oils belong to one single population and were derived from same source kitchen/bed. The differences in their chemical compositions and physical properties mainly result from secondary alteration of oils that were charged during the early phase of trap formation. The thickness of Upper Ordovician and Silurian caprocks of oil reservoirs in the Rewapu Block is higher than that in the north part of the Halahatang region, and therefore, significant biodegradation process is prevented. Compared to heavy oils in the north part, the Rewapu oils are dominated by light oils with no 25-norhopanes and no GC–MS ‘‘hump''(UCM: unresolved complex mixture) on the chromatographic baselines. The heavy oils in Wells RP7 and RP101 C were primarily influenced by water washing since apparent reduction of alkylated dibenzothiophenes was observed. The local geological background favored the water washing alteration. The reservoir geochemical study has practical application in hydrocarbon exploration and predicts the nature of oils in this oilfield.

Analysis of fretting wear behavior of unloading valve of gasoline direct injection high-pressure pump

The high pressures in gasoline direct injection technology lead to structural damage in some hydraulic components,especially annular damage on the contact area of the valve ball and on the valve seat of the spherical unloading valve in the high-pressure pump.In previous study,the authors have analyzed the damage on the unloading valve and demonstrated that it is caused neither by static damage nor fatigue damage and have put forward the hypothesis of fretting wear.This paper is based on the establishment of the statically indeterminate structure of the unloading valve.The micro friction parameters(stress,friction coefficient,etc.)required for the numerical iterative calculation of fretting wear are calculated.In addition,based on the grid adaptive technology and a modified Archard wear model,the fretting wear is calculated quantitatively and is in good agreement with experimental results.Based on that verification,the wear laws of the valve ball and valve seat under the same hardness,different contact angles,and different assembly stresses,are analyzed in detail,and reasoned suggestions for the structural design and assembly design of the ball valve are given.