Real-Time Determination of Filtrate Contamination During Openhole Wireline Sampling by Optical Spectroscopy

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe key objectives of openhole wireline sampling are to identify desired fluids and to collect representative formation samples. Optical methods such as visible -near-infrared spectroscopy (NIR) are used to identify and quantify mixed oil, water, and gas flows in-situ during wireline logging. In wells drilled with oil based muds (OBM) or synthetic based muds (SBM), differentiating crude oil from the filtrate base fluid is critical. The widely used current practice is to measure the increase in fluid coloration (by NIR) vs. time to qualitatively assess the increasing fraction of crude oil with pumping time. Here, we describe new methods of utilizing NIR log data to provide quantitatively during sampling the %-OBM contamination in the extracted fluid. In addition, these methods allow prediction of contamination at future times during the sampling job, thereby determining the effectiveness of further pumping. The significant improvement in sampling efficiency is demonstrated with several log examples. Finally, using our methods, mud performance in the downhole environment can be monitored and optimized in subsequent jobs.

Self-Similarity in Contamination Transport to a Formation Fluid Tester During Cleanup Production

“…9a in logarithmic coordinates. The interesting fact is that all contamination curves have the same envelope represented by a straight line with a slope −5/12 matching the empirical exponent obtained by Mullins and Schroer (2000) in processing field data. The deeper the invasion, the earlier the contamination curve deviates from this straight line η = −5/12 .…”

“…The approach to modeling contamination transport during cleanup production that is currently considered state of the art by the industry is based on the empirical model for the contamination evolution with time during the late phase of cleanup (Mullins and Schroer 2000). This model states that the contamination, defined as the concentration of mud filtrate in the produced fluid, must decrease with time as t −5/12 .…”

“…This behavior contradicts the analytical model (Hammond 1991), which is based on the pseudospherical flow and contamination transport, predicting faster decay of contamination η with time, namely as t −2/3 . Recently, numerical simulations (Alpak et al 2006) have confirmed the empirical law, η ∼ t −5/12 , but have not explained the existing contradiction between the theory (Hammond 1991) and field observations (Mullins and Schroer 2000). The effects of borehole orientation and the azimuthal position of the probe on the cleanup production have been recently investigated by Angeles et al (2008) using three-phase compositional simulators.…”

The Missing Link--Identification of Reservoir Compartmentalization Through Downhole Fluid Analysis

“…[7,8] The earliest DFA measurement consisted of obtaining GOR by measuring the dissolved methane vs. liquid oil fraction in a single-phase crude oil using the LFA* Live Fluid Analyzer. [11,15] The physical basis of this measurement is described in the literature. [9,13] Recent work has significantly improved the robustness and utility of this measurement.…”

“…Thus, the two tools together provide compositional analysis over a broad range of crude oils and condensates. The LFA monitors contamination utilizing the OCM algorithm and analyzes for gas using a gas refractometer and GOR [11]. The CFA, on the other hand, detects retrograde dew formation and gives GOR and fluid composition.…”