Micro-seismic fracturing monitoring technology inside
well is a key technology for the exploration and development of unconventional
fields such as shale gas and tight oil and gas. Compared with ground micro-seismic
fracturing monitoring technology, fracturing monitoring inside well is more
closer, more accurate and more clearly reflect the fracture length, fracture
height, and real-time extension in the fracturing process, so that, technicians
analyze and study the formation transformation more accurately, evaluate the
fracturing effect in real-time, and guide the fracturing parameters efficiency.
The adjustment of the plan reduces the period and cost of reservoir reform
monitoring, it is one of the most accurate, timely and informative monitoring
methods in the fracturing process.
Real-time monitoring: Check the fracturing effect,
analyze the fracture morphology in real-time, adjust the fracturing parameters
(such as pressure, sand volume, fracturing fluid, temporary ball plug, etc.),
monitor the casing change, guide the fracturing construction in real-time,
optimize the fracturing plan.
Fracturing evaluation: Provide fracture network
geometry, comprehensive analysis by combined with well logging, rock
geophysical parameters, seismic data and other information to evaluate the
fracturing effect and estimate the available oil and gas Stimulated Reservoir
Development application: Provide fracture space shape
and maximum main in-situ stress direction, etc. And provide important reference
for the layout of oilfield development well patterns (horizontal well spacing,
horizontal section length, fracturing classification and fracturing section
MultiVSP is long operation
time designed. Downhole geophones work at 0.25 millisecond sampling rate with
up to 12-level detectors. The geophones finish the monitoring items with more
fracturing intervals such as horizontal well fracturing and longer periods.
Wellsite micro-seismic monitoring and processing flow
Taking the wellhead of the monitoring well as the
origin of the coordinates, a unified fracturing monitoring coordinate system of
the fracturing well trajectory and the monitoring well trajectory is
established, and the relative coordinates of the geophone position and the
fracturing section are established.
Accurate positioning of micro-seismic events requires
a suitable velocity model. The initial velocity model usually uses sonic
logging and VSP.
logging speed & original speed models
Corrected velocity model
When the perforation position and original velocity
model are known, the velocity value of each horizon is adjusted according to
the detonating cord or perforation signal P-wave signal, combined with the
divided geological horizon, and the velocity model is adjusted multiple times
to make the rupture event Positioned at the detonating cord point.
The main purpose of the detonating cord or perforation
signal includes two aspects. One is to obtain the direction of the detector and
correct the original setting of the detector. The other is to verify the
rationality of the speed model, and make the necessary optimization and
Strong noise has caused interference to the signal,
the difference of characteristics in apparent speed and spectrum suppresses the
noise, which highlights the signal energy and improves the positioning accuracy
of the fracture event.
Screens effective fracturing event points, and provides
accurate phase expiration recognition based on the first arrival and peak
values of P-Wave and S-Waves.
Polarization analysis rotates the micro-seismic signal
into P, SH, and SV phases. The analysis signal source is a P-Wave source, a
SH-based source, or an SV-based source. The P-Wave is used to calculate the
location of the micro-seismic event.
Schematic diagram of
The difference method can identify P-waves and S-waves
for the monitoring records with relatively high signal-to-noise, and use P-wave
time difference method to retrieve the location of the fracturing event point.
For the monitoring records with low signal-to-noise
ratio, only P-Wave or S-Wave can be identified, and the location of the
fracturing event point can be retrieved using the same wave type time
Well 35-6, Stage 16
Well 35-5, Stage 16
Well 5, Stage 14
Well 5, Stage 16
Well 6, Stage 16
The b value
represents the extent to which an area is subjected to the average stress and
the receiving strength limit, and the stress state of the medium under the
action of the tectonic stress field. When the regional average stress
increases, the b value decreases, and conversely the b value increases.
Calculating the b values of this section in the two wells are 0.45 and 0.47
respectively, indicating that there are certain natural fractures in the
fracturing section. It is speculated that due to the good brittleness of the
formation, the early fracturing stimulated the formation activity. The degree
is affected by natural fractures.
Well 5, Stage 14-17, Joint Display
Well 6, Stage 15-18, Joint Display
Dual-Well Joint Display
monitoring results of eight sections in two wells show that the fracture length
of Well-5 is 282-327 meters, the fracture width is 59-64 meters, the fracture
height is 40-60 meters, and the direction is 63-76 ° from north to east. The
fracture length of Well-6 is 287 -338 meters, fracture width is 45-66 meters,
fracture height is 43-51 meters, direction is 66-86 ° from north to east.
micro-seismic events are mainly distributed in the formation stage of the main
fracture network. During this period, the micro-seismic events are intensive
and the energy is strong. The fracturing has obvious effect on the formation
monitoring results show that the east and west sides are basically
calculating the b value, there are certain natural fractures in the fracturing
section, and the development of the fracture network is affected by certain
(5) The multi-segment
joint display segment is relatively clear, and the perforation cluster spacing
is more reasonable.