Formation tester

One method of sampling reservoir fluids and taking formation pressures under reservoir conditions in open hole is by using a wireline formation tester. A number of wireline logging companies provide such a tool under the names such as RFT (repeat formation tester) and FMT (formation multi tester), so called because they can take a series of pressure samples in the same logging run. A newer version of the tool is called a modular dynamic tester or MDT (Schlumberger tool), shown in Figure 3.8. 

A good formation pressure agreement is seen at 9,500 ft with the wireline formation tester data. 

Limitations to the proper analysis of accumulation conditions were still formed by poor seismic resolution, unreliable pressure measurements and lack of sophisticated geochemistry. Until the wireline formation tester had reached such a state of development that it could provide reliable and repeatable pressure measurements, it was often difficult to recognise either separate or connected accumulations in the more complicated structures. 

Dake, L.P. 1982. Application of the repeat formation tester in vertical and horizontal pulse testing in the Middle Jurassic Brent Sands. Paper EUR 270, Proc. Eur. Offshore Pet. Conf. 1982. 

Fig. 9, Thi,s figure shows the pressure versus depth profiles for the discovery well shown in Fig. 8. Computed pressures from both seismic (predrill) and sonic (post-drill) velocities are shown and compared with the measured pressures from the repeat formation testers denoted by RFT. The overburden pressure was estimated from the seismic velocity and found to be in good agreement with that obtained from integrating the density log (post-drill).

Analysed gases and oils are bottom-hole samples unless otherwise indicated in the text or figures. Bottom-hole samples (BHS) and cores generally predate enhanced oil recovery activity (1979-1984), thus represent original field conditions. Exceptions include multiple dynamic formation test (MDT) oils, repeat formation tester (RFT) oils, sidewall cores (SWC), or separator oil samples from recent wells usually at the periphery of the field. 

Fluid pressure is one of the most common parameters measured in oil and gas reservoirs. Highly precise measurements—to the sub-psi (pounds per square inch) level—are commonly obtained using wireline tools such as the Repeat Formation Tester (RFT) or Modular Formation Dynamics Tester (MDT), both of which can measure pressure at numerous... 

Formation pressure data were obtained from repeat formation tester (RFT) or modular dynamic tester (MDT) measurements of numerous deep wells in the Central North Sea. These data were used as the primary pressure dataset as they are the most accurate pressure measurements possible down-hole. The MDT/RFT wireline tool takes a pressure reading within a permeable formation, by setting a seal at a precise depth determined by using an accompanying gamma ray tool for depth correlation. Drill stem test (DST), mudweight data and kick (influxes of pore fluids into the wellbore) information was also used where RFT or MDT data were not available or of very poor quality. A summary of the various approaches used to derive formation pressures is provided by Holm (1998). 

Thus, this boundary condition affects only one line of the tridiagonal matrix. Again, the volume flux at the farfield needwo/ equal Q(t), except at steady state. We will build upon the notions and ideas introduced here in the subsequent chapters, step by step, in order to introduce state-of-the-art ideas in modeling. In Chapter 18, exact solutions for spherical, transient, compressible flow with skin, storage, and anisotropy are developed for formation tester use. 

Fluid compressibility. Here we examine the effects of fluid compressibility on invasion. This should not be confused with mudcake and rock compressibility, which represent different physical phenomena. We consider a simple lineal flow example, which will be followed in Chapter 18 by an important and sophisticated formation tester solution useful in modem formation evaluation. We reconsider the liquid and gaseous lineal flows treated earlier, but this time, include the transient effects due to fluid compressibility in a homogeneous core without mudcake. The pressure P(x,t) now depends on both X and t. The relevant geometry is shown in Figure 17-9, where the left- and right-side pressure boundary conditions are P(0,t) = P/ and P(L,t) = P and L is... 

Formation testers are measurement instruments that retrieve reservoir fluid samples from wells during pauses in drilling operations. Various practical questions arise. A type of reverse invasion problem appears how long must pumps be operated in order to obtain true formation fluids and not mud filtrate contaminants How do pump power requirements vary in permeable versus tight zones Can measured pressure transients be interpreted for rock characteristics like permeability and anisotropy Different answers are obtained depending on the fluid model assumed. Later in this book, we will consider constant density, immiscible, two-phase flows with and without mudcake effects. For now we assume transient, compressible, single-phase flow, but within this framework, we formulate and solve a very general problem. 

Using the exact solution for transient ellipsoidal flow of compressible liquids in transversely isotropic media derived in Chapter 18, develop an interpretation method to determine kj, and k, assuming that pressure histories at the source probe and another observation probe are available. For typical formation tester pumping rates, what is the optimum transmitter to receiver probe separation for maximum pressure resolution ... 

In electromagnetic logging, phase delays between transmitter and receiver are used to predict resistivity. Starting with the diffusion model implied by Equation 18-5, show that, analogously, time delays between an oscillating formation tester piston and an observation probe can be used to predict permeability (Proett and Chin, 2000). 

Now let us rework the preceding cylindrical radial problem, and alter the analytical and numerical formulations so that they handle spherical radial flows. Such formulations model invasion at the drillbit and also point fluid influx into formation testers at small times. We will replace the governing equation for cylindrical radial flows, namely, d2p(r)/dr2 -i- (1/r) dp(r)/dr = 0 in Equation 20-33, by the spherical flow equation... 

Note that Multiple Factors That Influence Wireline Formation Tester Pressure Measurements and Fluid Contact Estimates, by M.A. Proett, W.C. Chin, M. Manohar, R. Sigal, and J. Wu, SPE Paper 71566, presented at the 2001 SPE Annual Technical Conference and Exhibition in New Orleans, Louisiana, September 30-October 3, 2001, extends the work in this chapter to higher order, ensuring that mass is accurately conserved at strong saturation discontinuities. For further information or a complimentary copy of the paper, the reader should write or contact the author directly at wilsonchin aol.com. 

Proett, M.A., and Chin, W.C., Advanced Permeability and Anisotropy Measurements While Testing and Sampling in Real-Time Using a Dual Probe Formation Tester, SPE Paper No. 64650, Seventh International Oil Gas Conference and Exhibition, Nov. 2000, Beijing, China. 

U.S. Patent No. 5,644,076. Wireline Formation Tester Supercharge Correction Method, with M. Proett and M. Waid, July 1,1997... 

Multiple Faetors That Influence Wireline Formation Tester Pressure Measurements and Fluid Contacts Estimates, with M. Proett, M. Manohar, R. Sigal, and J. Wu, SPE Paper No. 71566, SPE Annual Technical Conference and Exhibition, Oct. 2001, New Orleans, LA... 

Advanced Permeability and Anisotropy Measurements While Testing and Sampling Using Dual (Formation Tester) Probes, with M. Proett, 41st SPWLA Annual Symposium, Society of Professional Well Log Analysts, June 2000, Dallas, TX... 

Permeability Prediction from Formation Tester Phase Delay and Sonic Pulse Analysis, with M. Proett, GRl - SPWLA Research Forum on Permeability Logging, Feb. 1997, Flouston, TX... 

Badry R, Head E, Morris C, Travoulay I (1993) New wireline formation tester techniques and applications. SPWLA Annu Symp, Calgary, Alberta, June 13-16, 1993, pp H1-H15... 

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