AWD

Introduction

Dynamite was the only source used until 1953 when the weight dropping Thumper technique was introduced. Thumper’s advanced technology what we call AWD Automatic weight drop seismic energy source. But  Dynamite has serious drawback with respect to AWD handling safety, high drilling cost, logistical problems (villages, buildings and pipelines). Whereas Vibroseis requires many number in serial and a big crew running all the time, which also has a logistical issue(roads has to be conditioned more than that of AWD), whereas AWD can be mounted on a farm tractor or a heavy Russian Truck with minor modifications and easily implemented within a short time. Its problems are lesser in field with a single crew running for all mechanical issue, can be fixed with no time.

Basis for choosing a seismic energy source

1. Penetration of the required depth
2. Bandwidth for the required resolution
3. Signal to Noise ratio
4. Environment
5. Availability and cost

The AWDis a vehicle mounted, high performance gas-charged accelerated (impact) weight drop energy source designed for use on seismic exploration surveys. Applications include: shallow and deep refraction surveys, 2D and 3D seismic reflection surveys, Vertical Seismic Profiling (VSP), and downhole seismic or LVL surveys. Where applicable, the AWD is an environmentally friendly, economical, and efficient alternative to using dynamite and vibrator seismic energy sources. For many 2D and 3D seismic surveys that use explosives or vibrators as the primary energy source in only a portion of the survey area, the Digipulse can also be used as an “infill” source to obtain near offset data in cultural zones that may prohibit drilling and the use of explosives and large vibrators. Deeper multi-layer refraction and LVL, and VSP surveys can be conducted without the requirement for costly shot hole drilling and dynamite, or vibrator seismic sources.

AWD Operation is Estreme conditions and in a very difficult terrain

AWD Operation in Hilly terrain mounted on a Heavy Truck

Theory of Operation - The Physics of AWD

Unlike the explosive energy source, which is placed in shot holes below the ground, the AWD weight  drop is a surface “impact” type seismic energy source. The energy produced by the AWD (approximately 70 to 100 K-joules) is derived from a large hardened steel hammer mass (1180 lbs) that impacts a ground coupled base plate. The most important part is the coupling and the source synchronization with the instrument. The synchronization can be done through radio signal( minimum delay) or through wireline. A sensor attached to the base plate connected to a geophone sensing the earths vibration, is used for synchronizing with the instrument. Mechanically, the AWD uses a hydraulic system to lift the hammer mass to a “mass loaded” position. In the loaded position, a nitrogen gas charged cylinder and piston  assembly applies a downward force on the hammer mass. The approximate pressure applied to the hammer mass is a minimum 1,000 psi, depending on the model. Testings are carried on to adjust the Nitrogen pressure, which gives the best subsurface information. When released, the hammer mass is propelled at high velocity to impact the base plate. 

Conclusions

The concept of using weight drop, or accelerated weight drop technology, is not new to the seismic exploration industry. Several forms of weight drop systems have been in use for seismic exploration during the last 40 years. Currently, the AWD system is the only latest version of high performance accelerated weight drop systems in production. Depending on surface soil conditions, the source signature characteristics and energy levels of the AWD are usually sufficient for acquiring up to 4-6 second records (two-way travel time). Current users of the AWD report reaching target depths of up to 10,000 feet under ideal conditions. Typical seismic target objectives range from 2,000 to 15,000 feet.

AWD can deliver sufficient energy to reach shallow geologic target objectives, the AWD  1180 gas charged system is a more economical alternative in almost every aspect. A new AWD with a 3,000 lb mass mounted on an Minibuggy platform is now available. These larger Digipulse systems will deliver more than twice the downgoing energy of the Digipulse AWD units, and will likely reach the deeper seismic targets while still offering the same economical and production efficiency benefits.

The Digipulse AWD is also a more suitable source alternative in areas with sensitive cultural and environmental issues. In some cases, the AWD can be combined with  dynamite or vibrator operations to acquire only nearoffset data within areas that restrict or prohibit using energy sources that are hazardous or damaging to the environment. Moreover, the production rate in terms of completing a survey can be much higher, and the overall operating costs associated with the AWD is much less than with seismic surveys using dynamite or Vibroseis.