3.1 Oil content and molecular composition of shale fractions
3.1.1 Characteristics of oil content and molecular composition of fractions from frozen shale samples in situ
Characteristics of oil content and molecular composition of frozen (liquid nitrogen) shale samples collected by coring in drilling site(Fig. 1).The oil contents of S1-0, S1-1, S1-2, S1-3 and S1-4 fractions of 1620.43m deep shale samples from well cha21 are 1.25 mg / g, 0.44 mg / g, 0.33 mg / g, 0.31 mg / g and 0.38 mg / g, respectively.The main molecular compositions of the samples are nC1-nC9,nC1-nC15,nC12-nC20,nC15-nC22,nC18-nC26. It can be seen that the five temperature fractions are mainly gas, gasoline, kerosene, diesel oil and heavy oil(Department of organic chemistry,1984),the content of the samples was 46%, 16%, 12%, 11%, 15%,the main components are gas and gasoline.The parent material type is II1, and the maturity Ro is 0.80%,it is in the early stage of maturity.It can be seen that this kind of sample has the highest content of gas fraction.
3.1.2 Characteristics of oil content and molecular composition of fractions from conventional shale samples
Simultaneous analysis of oil content and molecular composition of shale fractions collected by core library show that(Fig.2),the oil contents of S1-0, S1-1, S1-2, S1-3 and S1-4 fractions of 1625.3m shale samples from well Pu53 are 0 mg / g, 0.04 mg / g, 0.17 mg / g, 0.44 mg / g and 1.42 mg / g.The main distribution of its molecular composition was not detected,nC11-nC15 (n-alkane degradation), nC13-nC17 (n-alkane degradation), nC15-nC20 (n-alkane degradation) and nC18-nC25 (n-alkane degradation) accounted for 0%, 2%, 8%, 21% and 69%.The n-alkanes of gasoline, kerosene and diesel oil were biodegraded,it is mainly composed of heavy oil and no biodegradation occurs.The type of hydrocarbon parent material is II1 and the maturity Ro is 0.83%,it is in the early mature stage of hydrocarbon expulsion.The oil contentof S1-0, S1-1, S1-2, S1-3 and S1-4 fractions of 2135.78m shale sample in well syy2 are 0 mg / g, 0.83 mg / g, 1.19 mg / g, 0.93 mg / g and 0.66 mg / g.The main distribution of its molecular composition was not detected.The contents of nC13-nC20, nC17-nC23, nC20-nC26 and nC23-nC29 accounted for 0%, 23%, 33%, 26% and 18%.It is mainly composed of kerosene, diesel oil and gasoline.The type of hydrocarbon parent material is II1 and the maturity Ro is 1.19%,in the mature stage.The oil content of S1-0, S1-1, S1-2, S1-3 and S1-4 fractions of 2557.36m shale samples from well Gy1 are 0.06mg/g, 0.63mg/g, 1.17mg/g, 1.27mg/g and 0.16mg/g.Its molecular composition is mainly distributed in nC10-nC13, nC11-nC16, nC12-nC18, nC13-nC21, nC15-nC20, and the contents were 2%, 19%, 35%, 39% and 5% respectively.It is mainly composed of diesel oil,the type of hydrocarbon parent material is type I,the maturity Ro is 1.67%, which is in the high maturity stage.It is seen that,the oil content and molecular composition of the fractions are different in different well shale samples of the first member of Qingshankou formation.It reflects the differences of shale with different parent material types and maturity.
3.2 Evaluation of oil bearing and fluidity of shale reservoir
3.2.1 Evaluation of oil bearing property of shale reservoir
The larger the oil content of shale fraction and its value, the better the oil-bearing property of reservoir,under the same analytical conditions.The oil content of shale in well cha21, Pu53, Gy 1 and syy2 is 1.33 mg / g, 2.09 mg / g, 3.29 mg / g and 3.61 mg / g.In terms of oil content, syy2 and Gy 1 are the best, Pu53 is the second, cha21 is the last (Table 1).But it should be noted that,although the oil content of well Pu53 is higher than that of well cha21, the components of gasoline, kerosene and diesel oil in the first member of Qingshankou formation in well Pu53 are biodegraded,the degradation of n-alkanes is serious, the crude oil becomes thicker and the oil quality is obviously worse.
3.2.2 Fluidity evaluation of shale reservoir
Under the same or similar reservoir physical properties, the larger the light component proportion and the smaller the heavy component proportion of shale oil, the better the reservoir crude oil fluidity.The gas fraction in the conventional shale sample is very easy to lose,therefore, we adopt (s1-1 + S1-2 + S1-3) / s1-4, that is (steam + coal + diesel) / heavy oil ratio (light weight ratio parameter),this parameter is relatively less affected by light hydrocarbon loss.We use this parameter to evaluate crude oil fluidity in shale reservoirs (Table 1).The light weight ratio of well cha21, Pu53, syy2 and Gy1 is 3.76, 0.45, 4.56 and 18.6,the order of liquidity was Gy1 > syy2 > cha21 > Pu53,their maturity Ro were 0.80%, 0.83%, 1.19% and 1.67%.Therefore, the higher the maturity, the better the fluidity of shale oil.However, the crude oil maturity RO of well Pu53 is slightly higher than that of well cha21, because of the degradation of crude oil in well Pu53, the fluidity of well Pu53 becomes worse. According to the results of exploration and test, the fracturing of cha21, syy2 and Gy1 shale can obtain industrial oil flow, so (steam + coal + diesel) / heavy oil ≥ 3 is taken as the evaluation boundary value of liquidity desserts.