What Is Sonic Drilling?

Acoustic logging refers to a logging method that uses the acoustic characteristics such as speed, amplitude, and frequency changes of different waves to study the geological profile of a well, and determines the quality of cementing.

A controlled acoustic wave source is placed in the well.The sound waves emitted by the sound source cause the surrounding particles to vibrate, generating body waves, i.e. longitudinal and transverse waves, in the formation, and induced interface waves, i.e. pseudo-Rayleigh waves, on the interface of the well wall and drilling fluid And Stone Lebo. As the carrier of formation information, these waves are received by downhole receivers and sent to the surface for recording, which is sonic logging. receiver,

Sonic logging is divided into sonic logging and sonic logging. Sonic logging measures formation acoustic velocity. Formation acoustic velocity is related to the lithology, porosity, and pore fluid properties of the formation. According to the propagation speed of sound waves in the formation, formation porosity, lithology, or pore fluid properties can be determined.

Acoustic velocity logging is referred to as acoustic velocity logging, which records the time required for acoustic waves to pass through a 1-meter rock formation, and measures the time difference t (reciprocal of the P-wave velocity of the formation) of formation sliding waves. It is mainly used to calculate formation porosity, formation lithology analysis, and judge gas layers. ^[2]

1. The different mineral composition of rocks is the main reason for the difference in sound velocity of rocks, that is, the lithology is the main factor that causes the sound velocity of rocks.

2. The sound velocity of porous rock formations is lower than the sound velocity of non-porous dense rock formations of the same lithology.

3. The sound velocity of sandstones with the same porosity is much higher than that of oily water. The larger the sandstone porosity is, the higher the sound velocity of the sandstone skeleton is. The sonic time difference is the largest.

4. The burial depth also affects the sound velocity. As the depth increases, the pressure of the upper abdominal stratum on the rock layer increases, which will change the particle density, elastic modulus of the rock, and the fluid density and elastic parameters in the pores. Yes, the porosity of the rock formation decreases with the increase of the depth of the overlying rock formation, which increases the sound velocity of the rock formation, that is, the time difference of the acoustic wave of the same lithological formation decreases. ^[2]

1. Division of strata

Because different strata have different sonic velocities, different lithological strata can be divided according to the sonic time difference curve. Sandstone sonics have large sonic velocities and small time lags; mudstone sonic velocities are small; dense limestone and Dolomite jet lag is low and muddy jet lag is increased. If there are cracks and pores, the jet lag is significantly increased. Sandstone is 55.5 us / ft (182us / m), limestone is 47us / ft (155us / m), dolomite is 43us / ft (141us / m), and fresh water is 189us / ft (620us / m).

2.Determining rock porosity

3.Identify gas layers and fractures

The sonic log curve shows a sharp increase in the time difference value. The increased value is multiplied by the period of the sonic signal (about 50 microseconds). This phenomenon is called "cycle hopping". The "cycle jump" can be used as a characteristic indicator of gas content in fractured intervals or reservoirs.

(1) The time difference generally increases, and it can generally be considered that the porosity in the same formation is more developed. However, if there is a geological basis for gas or fracture, it can also be judged as a gas or fracture zone.

(2) If the time difference is significantly increased or there is a frequency jump, local gas may contain gas, and the resistivity log shows that the formation contains oil and gas, which can be judged as a gas layer; gas cannot be contained on the local quality At this time, it can be judged that the fracture is abnormally developed; if there is a gas layer with fractures in the local layer, it should also be confirmed from resistivity logging and other data.

(3) Rock wells with severely enlarged boreholes or well sections with severe mud-mixed gas may also produce significant time differences or cycle jumps. ^[1]