Strike-slip
fault impact
zone | 1 | Distribution
of main and branch faults, scale of fault zone | Strike-slip fault impact zone formed under tensile,
compressive, and
shear stresses | Difficult to encounter
and identify due
to large scale | Obvious misalignment on the event, "Y" or "flower" shape
on seismic section, and the seismic coherence can identify abnormal boundaries | Extraction of seismic
coherence body attribute, automatic fault picking and human-machine interaction interpretation |
Fault-controlled
karst | 2 | External
geometric
morphology and scale | Area with relatively concentrated
dissolution in strike-slip fault impact area | Decrease of drilling
time obviously, acoustic wave and density values, and enlargement in well diameter | Bead-string, "V" or column shape on amplitude reflection, and seismic amplitude or energy attributes are more sensitive, and have usually obvious abnormal responses to fault-controlled karsts | Seismic maximum
likelihood attribute or structure tensor, seismic target delineation and extraction technology |
| Fracture and cave zone in fault-controlled karst | Large cave | 3 | Morphology, location and scale | Fairly strong-
strong dissolution, primarily large caves | Drilling fluid loss or unloaded drilling tool, obvious reduction of
drilling time, and
obvious changes
on resistivity and
density curves | Greater than 5 m in average diameter, they have obvious bead-string shape in amplitude, and "drop-like" characteristic. They can be identified easily by seismic energy or structure attributes | Combination of outcrop, drilling and logging, [seismic] facies, drilling calibration, seismic structure inversion attributes, attribute truncation and target extraction technology |
| Dissolution pore zone | Morphology, location and scale | Weak-medium
in dissolution, the fracture and cave zone has primarily small pores | Obvious changes
on resistivity and
density curves,
and dark shapes
on FMI images | With diameter of centimeters on average, dissolution pores are difficult to identify individually. Seismic energy attributes can roughly identify the distribution of dissolution pore zones, and dissolution pore zones would cause slight abnormal reflections on
seismic amplitude | Combination of outcrop, drilling and logging, [seismic] facies, drilling calibration, seismic structure inversion attributes, attribute truncation and target extraction technology |
| Fracture-dense zone | Classification, location and scale | Tectonic stress or dissolution stress
is the main cause, and the fractures have no obvious enlarged dissolution | Obvious changes
in acoustic time
difference curve,
clearer FMI
imaging | With no obvious changes in amplitude and weak energy, individual small fractures are difficult to identify, but the they have obvious responses on seismic curvature or ant body attribute | Combination of core outcrop, logging, and [seismic] facies, the core outcrop statistical law constraint, seismic ant body and thinned fault likelihood (TFL) attribute, automatic fault extrac-
tion technology |
| Cave filling | 4 | Filling lithology, contact relationship | Affected by later mechanical or chemical filling,
large caves have
a greater impact
on the properties
of the reservoir | The difference in filling lithology is shown by different logging combination responses, usually the natural gamma and resistivity curves are more sensitive to the filling lithology | Affected by the shielding of the cave boundary, it is difficult to identify the seismic reflection characteristics of the filling in the caves. When the cave is large and filled with mud, some seismic inversion
attributes can be referred to | Combination of core
outcrop, logging, and [seismic] facies, primarily relies on logging interpretation, seismic wave impedance can be used to predict filling conditions tentatively |