D. Wright

Improving Signal-to-Noise Ratio Using Pseudo Random Binary Sequences in Multi Transient Electromagnetic (MTEM) Data

We present multi-transient electro-magnetic (MTEM) data using a step-function and a pseudo-random binary sequence (PRBS) as the source time function. We may recover the earth impulse response from either data set and integrate the result to obtain the corresponding step response. Results show that the PRBS waveform recovers the same result as the step in current but in a much shorter time.

Multi-transient EM Repeatability Experiment over Harding Field

We present results of a multi-transient electromagnetic (EM) repeability experiment conducted over the North Sea Harding field in 2007 and 2008. The segment of the field under investigation had produced 3.9 MMbbls of oil during this time. Processing of t

Successful Transient EM Survey In the North Sea At 100 M Water Depth

We describe the acquisition, processing, and interpretation of a successful transient electromagnetic survey acquired in water 100 m deep in the North Sea with a 30-channel seafloor receiver cable and bipole current source. The equipment was deployed along several lines to record data with very dense subsurface coverage: source-receiver offsets in the range 1,000 – 6,000 m with 200 m increments and mid-points every 100 m. Data quality was appraised and processed in real time. A special feature of the processing was removal of the air wave, which allowed the data to be inverted for subsurface resistivities using tried and tested algorithms. We present the results, revealing a promising target, and step-by-step processing and inversion of the data.

Travel Time to Resistivity Mapping Using the Multi Transient ElectroMagnetic (MTEM) Method

D041 Travel Time to Resistivity Mapping Using the Multi Transient ElectroMagnetic (MTEM) Method D. Wright* (MTEM Ltd) & A. Ziolkowski (MTEM Ltd) SUMMARY The time of the peak of the earth impulse response in multi-transient electromagnetic (MTEM) data can be mapped directly to an apparent half-space resistivity. The vertical resolution of this technique is poor. The gradient of the travel time moveout curve has the potential to yield an apparent interval resistivity. However direct mapping of the gradient suffers from large errors due to small errors in picking the time. These errors can be greatly reduced by applying a polynomial

Estimation of Induction Noise in a Towed EM Streamer

Towed-streamer receivers are in use for efficient acquisition of controlled source electromagnetic (CSEM) data. We investigate the contribution to the noise made by voltages induced, according to Faradays law of induction, in the telluric cables moving in the Earths magnetic field. We consider the Earths magnetic field to be spatially-invariant over the length of the receiver cable, and consider it to be either constant, or time variant. If the cable is straight behind the vessel, following the ships track, there is no induced voltage. If there are cross-currents and if the Earths magnetic field is time variant, there can be induced voltages which increase which the feathering angle, the length of the electric dipole receiver, and the magnitude of the rate of change of the magnetic field. Using a maximum feathering angle of 10° and the dipole length of 1100 m, the estimated noise is about two orders of magnitude less than the measured noise. We conclude that this is not the main source of noise. There must be some other mechanism causing the dominant component of the noise.

3-D Time-lapse Modelling and Inversion of Multi-transient EM Data over the North Sea Harding Field

We present results of a 3-D time-lapse multi-transient electromagnetic (EM) modelling experiment conducted over the North Sea Harding field. The reservoir model petrophysical parameters of porosity and fluid saturation were converted to resistivity using

Redevelopment of the Deep Tuscaloosa Gas Trend: A 3-D Seismic Case History of Judge Digby Field; Pointe Coupee Parish, Louisiana

ABSTRACT In October 1996, Amoco Production Company completed the Parlange #5 well in Judge Digby Field with an initial flow rate of 18 million cubic feet per day (MMCF/D) and 460 barrels of condensate. This well marked a new phase in Amocos continuing successful redevelopment of Deep Tuscaloosa gas fields using modern 3-D seismic technology. Since implementing 3-D technology, Amoco has drilled 15 consecutive discoveries, in areas once thought to be near the end of their productive lives. 3-D seismic technology has added value to the Tuscaloosa gas fields by defining untested fault blocks in known productive intervals and illuminating previously unseen deeper gas sand packages. This technology has also helped Amoco avoid the costly and potentially catastrophic drilling of depleted reservoirs, where current pressures are in the 4000 pounds per square inch (psi) range. Additionally, 3-D seismic has provided a tool for better prospect risk assessment, leading to better decisions for very expensive, deep wells, where dry hole costs average about

Multi-transient EM technology in practice

7,000,000. In Judge Digby Field, 3-D seismic has been directly responsible for gross gas reserve additions of over 200 billion cubic feet (BCF). The Amoco Parlange #5 is currently the deepest commercial gas well in the state of Louisiana with the deepest perforations at 21,500 ft. Amocos Deep Tuscaloosa redevelopment program continues today in Judge Digby, False River, and Profit Island Fields.