Nader Dutta

Geopressure prediction using seismic data: Current status and the road ahead

The subject of seismic detection of abnormally high‐pressured formations has received a great deal of attention in exploration and production geophysics because of increasing exploration and production activities in frontier areas (such as the deepwater) and a need to lower cost without compromising safety and environment, and manage risk and uncertainty associated with very expensive drilling. The purpose of this review is to capture the “best practice” in this highly specialized discipline and document it. Pressure prediction from seismic data is based on fundamentals of science, especially those of rock physics and seismic attribute analysis. Nonetheless, since the first seismic application in the 1960s, practitioners of the technology have relied increasingly on empiricism, and the fundamental limitations of the tools applied to detect such hazardous formations were lost. The most successful approach to seismic pressure prediction is one that combines a good understanding of rock properties of subsurf...

Detection and estimation of gas hydrates using rock physics and seismic inversion Examples from the northern deepwater Gulf of Mexico

Natural gas hydrates, composed primarily of water and methane, are solid, crystalline, ice-like substances found in permafrost areas and deepwater basins around the world. As the search for oil and gas extends into ever-deeper waters, particularly within the northern Gulf of Mexico, gas hydrates are becoming more of a focus in terms of both safety and as a potential energy resource.

Deepwater geohazard prediction using prestack inversion of large offset P-wave data and rock model

Successful deepwater drilling is defined as reaching the total well depth in the desired hole size safely (i.e., not exceeding the fracture pressure) while controlling hydrocarbon or water influx and ensuring that casings are placed across desired intervals. The oil and gas industry has succeeded in this mission thousands of time around the world but drilling challenges abound, especially in deepwater.

Combining rock physics analysis, full waveform prestack inversion and high-resolution seismic interpretation to map lithology units in deep water: A Gulf of Mexico case study

A successful seismic-based reservoir properties estimation effort has three steps: accurate seismic inversion in 3D to obtain relevant reservoir parameters, rock physics transformation to relate reservoir parameters to the seismic parameters, and mapping these parameters in 3D. This problem is nonunique and thus any available information—specifically geologic interpretation—should be used to improve our ability to infer the reservoir properties of interest with confidence. Moreover, uncertainty associated with the different predicted values (i.e., confidence interval and estimate of misclassification probability) must be provided as well, so that proper decisions can be made. Thus, it is evident that this involves interdisciplinary effort that includes rock physics, geologic interpretation, and seismic inversion technology. However, for quantitative description of reservoir properties, one must derive a way to quantify the errors and uncertainties associated with the process.

Shallow water flow prediction using prestack waveform inversion of conventional 3D seismic data and rock modeling

Shallow water flow (SWF) layers are frequently encountered in deepwater areas when drilling into poorly consolidated geopressured sands (Figure 1). These sands, when flowing, can cause extensive damage to a borehole. More than

Estimation of formation fluid pressure using high-resolution velocity from inversion of seismic data and a rock physics model based on compaction and burial diagenesis of shales

200 million has been lost to date for remediation and prevention of SWF problems in the Gulf of Mexico. Lately, this problem has also been a concern in many other deepwater clastic basins in the world. Figure 1. Shallow water flow problem encountered in deepwater drilling. SWF sands are known to occur in water depths of 450 m or more and typically 300–600 m below the mudline. They are known to be present in almost all deepwater ocean basins where the rate of sedimentation is high. Figure 2 shows the formation of SWF layers in a deepwater environment. Loose and unconsolidated sediments with a high rate of sedimentation characterize the overburden and low permeability seal is created by compacted shales or mudstones for which the rate of sedimentation is low. If isolated sand bodies are in this shale or mudstone, water from such bodies will not escape easily due to the presence of low-permeability sediments around them. In addition, the high rate of sedimentation from the overburden exerts an enormous pressure on these sediments, causing these isolated bodies containing large amounts of water to be overpressured. These overpressured SWF layers pose a threat to drilling, and their identification prior to drilling is therefore important in reducing risk. In this paper, we study the feasibility of detecting SWF layers using prestack waveform inversion of seismic data in conjunction with geologic analysis of stratigraphic sequences related to SWF zones. Figure 2. Formation mechanism of SWF sands. In-situ measurements of elastic and other rock properties of SWF sediments are very limited because SWF layers are associated with very low sonic velocities. Measurement of such …

Role of 3D seismic for quantitative shallow hazard assessment in deepwater sediments

Accurate assessment and prediction of formation fluid pressure and fracture gradient form an essential part of the planning process during various phases of hydrocarbon exploration and exploitation; these include regional basin analysis and basin high-grading, prospect identification, analysis, and drilling campaign to lift hydrocarbons. While the literature is full of activities in this field that are linked to the need for drilling safety by providing help with casing and mud weight program—and quite justifiably so—very little discussion addresses another, and very important need: seal integrity and trap configuration analysis.

Building a Seismic-driven 3D Geomechanical Model In a Deep Carbonate Reservoir

Increased drilling activities in deep water since 1985, especially in the Gulf of Mexico (GOM), have revealed numerous hazards in the shallow sediments below the seabed, such as fault scarps, gas vents, unstable slopes, and reefs and shallow subsurface geologic hazards such as faults, gas-charged sediments, buried channels, abnormally pressured sands, and gas hydrates. Drilling risks associated with shallow aquifer-pressured sands or shallow water flow (SWF) sands and gas hydrates have received the most attention. These are global problems. In the GOM alone, more than US

High-resolution pore pressure prediction using seismic inversion and velocity analysis

250 million has been lost due to SWF. While the industry has matured in handling these problems, it is estimated that the losses associated with SWF sands continue to be nearly

Propagating seismic data quality into rock physics analysis and reservoir property estimation: Case study of lithology prediction using full waveform inversion in clastic basins

1.7 million per well in the GOM alone.