EXPLORATION &
DEVELOPMENT
further limit fluid-type identification.
For intermediate-basic rock and acid rock, Vp/Vs ratios
are 1. 83 and 1. 75, respectively, which effectively distin-guishes gas and water zones. But low porosity makes distinguishing between gas zones and gas-water coexistence zones
difficult. Elastic wave velocity measured via the ultrasonic
pulse method can reveal the physical mechanisms identifying gas and water zones in igneous rock. This article also
links the physical mechanism to the internal factors of these
reservoirs, further identifying fluid types.
The study described in this article obtained Vp and Vs of
igneous cores from Junggar basin in dry and water-saturated states to determine other internal influences on elastic
wave velocity such as lithology, porosity, and density. Analysis shows that gas-bearing formations will decrease both Vp
and Vp/Vs ratio but with only a small impact on Vs, which
provides the physical basis for identifying of gas and water
Jun Jia
Liqiang Sima
Liang Wang
Southwest Petroleum University
Chengdu, China
Hui Zhao
Chuanqing Drilling Engineering Co. Ltd.
Chengdu, China
Crossplots of elastic wave velocity and resistivity can identify gas and water zones in tested formations of northwest
China’s Junggar basin. The Junggar basin features low-porosity igneous formations, which can make fluid types difficult to identify, longitudinal (Vp) and transversal wave velocities (Vs) being weakened in gas and water zones. Complex
lithologies and greater silica (SiO2) content in igneous rocks
Elastic wave velocities identify igneous
gas, water layers in Junggar basin
ELASTIC WAVE VELOCITY TEST Table 1
––––––––––––– Saturated –––––––––––– –––––––––––––––––– Dry ––––––––––––––––
Density, g/cc Vp Vs Vp/Vs Density, g/cc Vp Vs Vp/Vs Test Sampling No. Lithology Porosity, –––– km/sec –––– –––– km/sec ––––
1 00429 0.2 3.02 3. 87 2. 11 1. 83 2. 81 3.08 2.02 1. 52
2 05640 2. 1 2. 85 3. 36 2. 11 1. 59 2. 66 3. 19 2. 33 1. 37
3 16487 Basalt 14. 8 2. 80 3. 88 2. 17 1. 79 2. 41 2. 74 1. 46 1. 88
4 16488 13. 7 2. 74 4.02 2.05 1.96 2. 35 2.44 1.97 1. 24
5 04678 15. 3 2. 68 2. 38 1. 45 1. 64 2. 29 2. 36 1. 49 1. 59
6 04673 Andesite 13.0 2. 62 2. 53 1. 61 1. 57 2. 27 2. 50 1. 48 1. 69
7 04400 1.0 2. 69 4. 24 2. 74 1. 55 2. 54 3. 29 2. 19 1. 51
8 04404 2. 6 2. 54 3.99 2.00 1.99 2. 36 3.09 2.01 1. 53
9 20321 8.0 2. 74 3.02 1. 89 1. 59 2. 46 3. 17 1. 75 1. 82
10 05568 Diorite-porphyrite 9. 2 2. 64 3. 86 2. 12 1. 83 2. 37 2. 90 1. 83 1. 59
11 05579 9. 9 2. 60 3. 45 1. 88 1. 84 2. 33 2.96 1.93 1. 54
12 20329 11. 1 2. 66 3.01 1. 79 1. 68 2. 40 3. 17 1. 80 1. 76
13 06103 6. 8 2. 62 4. 20 2. 53 1. 66 2. 39 3. 79 2. 46 1. 54
14 06106 Granite-porphyry 3. 3 2. 64 3. 91 2.05 1. 91 2. 45 3. 41 2.06 1. 66
15 06109 8. 7 2. 64 2.95 1. 80 1. 64 2. 37 2. 91 1. 84 1. 58
NONLINEAR RELATIONSHIP, ρ AND V Table 2
––––––––––––––––––––– ρ-Vp ––––––––––––––––––––– ––––––––––––––––––– ρ-Vs ––––––––––––––––––––
Lithology Regression formula Correlation coeffcient Regression formula Correlation coeffcient
Basalt ρ= 1.349Vp0.608 0.89 ρ= 2.191Vs0.232 0.55 Andesite ρ= 1.795Vp0.269 0.87 ρ= 2.087Vs0.218 0.89 Diorite-porphyrite ρ= 1.541Vp0.394 0.80 ρ= 3.251Vs-0.512 0.94 Granite-porphyry ρ= 2.269Vp0.049 0.37 ρ= 2.378Vs0.016 0.14
