METHOD OF MINIMIZING IMMISCIBLE FLUID SAMPLE CONTAMINATION

Abstract

A method of formation fluid sampling that includes setting a dual packer tool in a wellbore. The dual packer tool is used to isolate an interval between an upper packer and a lower packer. The method also includes drawing fluid from the interval with a lower inlet, until an oil fraction increases over a base line reading, and drawing oil from by pumping at a low rate with an upper inlet.

Claims

1. A formation fluid sampling method as described and show.

2. A method of formation fluid sampling, comprising: a. setting a dual packer tool in a wellbore; b. isolating an interval between an upper packer and a lower packer; c. drawing fluid from the interval with a lower inlet, until an oil fraction increases over a base line reading, and drawing oil from the interval by pumping at a low rate with an upper inlet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0007] FIG. 1 depicts a dual packer sampling tool in a borehole.

[0008] FIG. 2 depicts a schematic of an embodiment of a method of formation fluid sampling.

[0009] FIG. 3 depicts dual flow line architecture allows for maximum flexibility of placement of the subsystems (pumps, fluid analyzer and sample bottles) with respect to the dual packer.

DETAILED DESCRIPTION

[0010] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would still be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0011] When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0012] FIG. 1 depicts a dual packer sampling tool in a borehole. The dual packer tool can have an upper inflatable rubber element and a lower inflatable rubber element. The dual packer tool has at least two inlets between the inflatable rubber elements. The inlets are in communication with an isolated interval. During formation testing applications fluid is pumped out from the isolated interval and can enter the tool though either of the two inlets. The interval is initially filled with drilling mud. As the fluid is pumped out of the interval it is replenished by the formation around the interval. The replenishing fluid is initially drilling mud filtrate followed by the reservoir fluid. The density difference between the formation fluid and the drilling mud filtrates will make the fluid phases segregate within the isolated interval. In non-horizontal wells, the level of the interface between the fluid phases can be controlled by pumping from one inlet. The aim is to submerge the other inlet completely in the phase that one desires to sample and thus eliminate any filtrate contamination.

[0013] FIG. 2 depicts a schematic of an embodiment of formation fluid sampling. The method can include pumping drilling mud that is in the isolated interval using the lower inlet. As drilling mud is removed from the isolated interval it is replaced by mud filtrate. The lower inlet is in communication with a first flowline inside the dual packer tool body, and the upper inlet is connected to another flow line. A fluid analyzer identifies the flowing phases in both flow lines. Filtrate break through is observed when the interface between the filtrate and the drilling mud reaches the lower inlet. At this point the pump that is connected to the upper inlet may be turned on at a low rate. Clean-up pumping continues from the lower inlet to continuously lower the filtrate/oil interface below the upper inlet. When the formation oil reaches the lower inlet the top inlet is fully submerged in oil. Sampling is conducted when observe substantially pure oil is coming from the top inlet. Substantially pure oil can be when the contamination level is below a predetermined threshold, for example, the predetermined threshold can be 0.1 percent, 0.2 percent, 0.3 percent, 1 percent, 2 percent, 5 percent, 10 percent, or any other percent of contaminate that is predetermined. One skilled in the art with the aid of this disclosure would know how to determine the threshold and appropriate value thereof.

[0014] The method includes pumping from the lower inlet. At the time the oil fraction increases over base line reading at the lower inlet, the Line 1 pump from the upper inlet is turned on and oil is skimmed off at a low rate. For a heavier phase (e.g. water in oil based mud), the same strategy applies, but the role of the upper and lower inlet is reversed.

[0015] FIG. 3 depicts a dual flow line architecture that allows for maximum flexibility of placement of the subsystems (pumps, fluid analyzer and sample bottles) with respect to the dual packer. The two flow lines run the length of the tool. The fluid analyzer, pumps and sample bottles can be placed above or below the dual packer or a mixture of above and below. The pump rates and direction is controlled individually over a wide range of flow rates and differential pressures. Inter-tool communication and downhole processing is utilized to automate the entire process. Inflation of the packer elements can be done automatically. Inlet valves and pumps may be controlled in accordance to the observations on the fluid analyzer. Fluid phases in the fluid analyzer can be determined using now known or future known techniques. The timing of how to control the pumps and inlet valves are based on the flowing fraction. FIG. 3 depicts the fluid fractions of both flow lines: the top plot shows the flowing fractions coming from the upper inlet and the lower plot shows the fluid fractions coming from the lower inlet.

[0016] The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.