Method for Characterizing Subsurface and Optimizing Well Placement
Publication Date: 2011-Aug-10
The IP.com Prior Art Database
Page 01 of 5
METHOD FOR CHARACTER IZ ING SUBSUR FACE AND OPTIMIZ ING WELL PLAC EMENT
A B S T R A C T
The primary embodiment is to make maximum use of surface seismic, borehole seismic, wireline, and other data to reduce uncertainty in the description of the sub-surface, and to further use this model to improve the determination of rock properties including thickness, resistivity, etc., to optimally place a wellbore in the overburden and the reservoir.
B A C K G R O U N D
Wellbores drilled through earth formations to drain reservoir fluids are frequently drilled along a deviated or horizontal trajectory. Since oil and gas reservoirs are frequently located in layered earth formations, the position of the deviated and horizontal wellbores with respect to the boundaries of the layers in the earth formations often has a significant impact on the productivity of such wellbores. Estimation of distances to layer boundaries, therefore, is important for landing in the reservoir as well as the positioning of the wellbore within the reservoir layers.
A common technique for determining the position of the wellbore with respect to layer boundaries generally relies on well log measurements from a nearby ("offset") well or a "pilot" well. The log measurements from offset and/or pilot wells are typically used to construct a sub-surface structural model that encompasses the extent of the planned well. Interpretations from surface seismic may be used to further constrain the layer thickness and layer boundaries between offset wells. Layer properties are typically interpolated between the wells using one of the many interpolation and geo- statistical techniques established in the industry. This represents a pre-drill model. The measurements obtained from wireline or other appropriate tools are typically compared to the model to optimize the positioning of the wellbore within the reservoir layer, and to maximize the length of the wellbore that is placed within a "target" layer or layers with desirable properties - such as distance from a boundary or fluid contact, oil or gas saturations, etc.
Page 02 of 5
Electromagnetic (EM), Sonic and other logging tools have been employed in subsurface exploration and well placement for many years. Well placement in real-time using resistivity measurements has been used by the industry since the availability of appropriate tools. During well placement, estimation of the borehole position with respect to known and expected geological markers is performed through correlation of various log measurements. Electromagnetic (EM) measurements are the most common measurements employed during well placement. These logging tools or instruments each have an elongated support equipped with antennas that are operable as sources (transmitters) or sensors (receivers). The antennas on these tools are generally formed as loops or coils of conductive wires. In operation, a transmitter antenna is energized by an alternating current to emit EM ene...