A Method of Formation Testing on Logging Cable

M. lEBOURG R. Q. FielDS SCHLUMBERGER WEn SURVEYING CORP. C. A. DOH HOUSTON, TEX. MEMBERS AIME

T. P.4635 Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021

ABSTRACT 1. Determination of productive fluid-particularly differentiating between gas and oil. A formation tester run on logging cable is now avail­ 2. Determination of reservoir pressu:re as an aid to: able to the oil industry. It offers a method of safely and (a) safety in completion technique, (b) reduction rapidly testing possible producing formations in uncased in drilling costs, and (c) reservoir analysis. holes. These tests can be made up the hole after run­ 3. Determination of minimum gas-oil ratios. ning the electric log. Reservoir pressure data is con­ 4. Location of gas-oil or oil-water contacts. tinuously recorded at the surface as the fluid sample 5. Recovery of samples for examination and analy­ is extracted. The tester may be assembled with a reser­ sis: oil (gravity); gas (hydrocarbon content); water voir of 1-, 2.75-, or 5.5-gal capacity. (salinity). A retaining pad on the body of the tool is expanded Additional applications envisioned for the future are against the wall of the hole at the exact depth desired; also given: (I) subsurface exploration based on accurate this depth is determined by electrical log control. Two pressure, (2) recovery of fluid samples from the undis­ bullets are then fired through the center of the retaining pad which create a connection between the formatieJ11 turbed reservoir for PVT work, and (3) possible quan­ and a flow line to the sample chamber. When the titative study of permeabilities or productivity index. chamber is filled, a valve is closed and the .fluid sample Running the formation tester requires no special pre­ sealed at maximum pressure. The tool is retracted to cautionary measares. Because full hydrostatic mud pres­ minimum diameter and brought out of the hole. Elec­ sure is maintained at all times, well depth is no problem. trical circuits permit a complete recording at the surface Thus, the method allows safe, economical testing in of the mechanical operations of the tool as well as the wells which heretofore could only be tested by setting formation pressure build-up and the hydrostatic mud casing. pressure. INTRODUCTION The tool was introduced commercially during the latter part of 1955 in the Gulf Coasts of Louisiana and A new method of safely and rapidly testing possible Texas. Over 1,000 operations have been made to date producing formations in uncased holes is achieving con­ (Sept. 1, 1956); 50 per cent of which resulted in suc­ siderable success. The method offers promise of further cessful tests. Failures have been due mostly to ineffec­ advances in reservoir study. Called the formation tester, tive sealing in ulnconsolidated sands. the new instrument is unique in that it operates on log­ One major company had 41 successful tests out of 80 ging cable. It thus offers all the advantages of wire-line attempts with 23 ineffective pad seals. Results for this operations and becomes an important adjunct to present company were very gratifying as to pinpointing gas-oil logging and side-wall coring services. The tester is ratios, indicating productive permeabilities and aiding in operated against the wall of the hole at any depth determination of fluid content where electrical log and desired. Zones to be tested are usually determined by side-wall coring information were inconclusive. a study of the electrical and the micro-caliper surveys. Eight typical pressure curves are discussed (including Reservoir data, as well as the operating cycle of the misruns). tool in the hole, are continuously recorded at the sur­ Six types of fluid recoveries are interpreted. face during the operation. The tester, as it was original­ Eight actual field examples of electric logs, showing ly designed, was capable of recovering a 1-gal sample the problems solved by the formation tester, are illus­ of reservoir fluid per trip in the hole. Tools with reser­ trated. voirs of 2.75- and 5.5-gal capacity are now available. The present applications of the tool are discussed: The 5.5-gal reservoir is equipped with a segregating system, set before going in the hole, so that the last Original manuscript receive« in Society of Petroleum Engineers office on Sept. 2'5, 1956. Revised manuscript received March 22. portion of the recovery (usually 1 gal) is automatically 1957. Paper presented at Petroleum Branch Fall Meeting in Los Angeles. Oct. 14-17, 1956. separated from the first portion. This makes it possible SPE-701-G PETROLEUM TRANSAcTIONS, AIME 260 to recover clean fluid in the final portion rather than formation through the perforations and connecting a mixture of filtrate and formation fluid. tubes to a sample chamber in the lower section of the It should be noted that open hole conventional tool. The enlarged view in Fig. 1 shows the seal mech­ drill-stem testing has not been practical in the deep anism in detail. Here the seal shoe, back-up shoe, Miocene welIs of Louisiana, where the danger of stick­ actuators, and flow line leading from pad to sample ing the packers and drilI pipes is serious. This leads chamber are clearly seen. The sample of formation to considerable perforating and casing drill-stem testing. fluid can thus be produced in a manner quite similar These operations are very expensive and can easily be to producing through perforated casing. reduced with the introduction of the formation tester 1 Gal. 2% Gal. 51;' Gal. operated on a logging cable. length ...... i6ft. 29 ft. 29 ft. While electric and auxiliary logs give considerable in­ Tool Diameter-Seal Unit .. . __ ...... 4 in. 4 in. .4 in . Tool Diameter.Sample Unit ...... " .4 in. .4 in. 5 in . formation, many companies and regulatory bodies do Maximum Diameter Seal Unit...... ___ 6 in. 6 in. 6 in. Minimum Hole Size . . __ __. ___ ...... __ ._ 77/8 in . 7 7/. in. 7 7/. in. not credit physicalIy untested reservoirs to their re­ Maximum Hole Size .. _._ ...... ______. __ __. .12 in. 12 in. 12 in . serves. A particularly difficult problem consists in the differentiation between oil and gas reservoirs. Fig. 2 is a schematic drawing of the tool. At the top is represented the pad expanding and contracting These considerations would point to the interest of a mechanism with its coupling to the cable for surface testing 'tool more flexible than the present drill-stem control, as well as the recording of operational and test, which could be run in conjunction with electrical reservoir data. The control mechanism in the tool is logging. essentially a relay which enables the performing of The purpose of the present paper is to describe this more than one phase of the operating cycle on a single Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 new instrument, the formation tester, to explain how cable conductor. The pad-expanding mechanism is an its data can be interpreted in terms of formation char­ electro-mechanical-hydraulic system. Next below is de­ acteristics and to discuss the assistance it can provide picted the seal section with its seal pad, back-up shoe, in reservoir evaluation. actuators, and return springs. When the surface controls indicate that the sample DESCRIPTION OF EQUIPMENT AND container is filled, the seal valve is actuated, sealing the OPERATING PROCEDURE sample at the maximum attained pressure. The closing of the seal valve is coupled automaticalIy to the col­ The tester is attached to the logging cable and ad­ lapsing mechanism of the tool; however, even though justed to its collapsed position. When assembled it the tool contracts, the seal pad usually remains stuck appears as in Fig. 1. It is lowered rapidly into the hole to the formation, holding the entire tool fast in place. until opposite the formation to be tested. By observing This is caused by the differential between the pressure the trace of the SP curve on the recorder screen, the of the mud column and the formation pressure. In the tool is positioned accurately at the depth desired as pad-gun block, along with the perforation charges for indicated on the electrical log. The tool is then ex­ establishing flow channels, are also two chambers termed panded, forcing a retaining pad against the wall of the "get-away guns." When the pad continues to stick to hole to form a seal between the mud column and the the walI, after collapsing the tool, these get-away shots formation. Two perforating bullets are fired from are fired-admitting the mud pressure to the outside chambers within the pad through its face and into the face of the pad. The pressure equalization, together formation. This establishes flow channels from the with the shock of the shots, breaks the pad away from the wall. With the sample sealed in the chamber and the tool free in the hole, the sample pressure gauge is now open through the sample line and perforated pad to the hydrostatic mud pressure which is recorded at the surface. The tester is then pulled out of the hole for measur­ ing and analyzing the sample. The surface recording may best be explained by examining the recording of an actual test; one made at a depth of 11,000 ft in a South Louisiana well. Fig. 3, Curve No.1, indicates the opening and closing of the pads (mechanical action applied to the

CABLE T,OOL OPER. INDICATOR PAD "SURFACE RECORDING EXPANDING - - - MECH. RETURN SPRI1GS BACK - UP­ SHOE

FLOW­ <~:~·.} BULLETS S~g:ON LINE PERFORATING J! GUNS . SEAL VALVE SURFACE RECOR DING

SAMPLE CHAMBER SAMPLE GAUGE (CONTROLLED FLOW)

FIG. I-FoRMATION TESTER. FIG. 2-SCHEMATIC DIAGRAM OF FORMATION TESTER.

261 VOL. 210, 1957 OF TEST pressure, is governed by the controlled flow mechanism in the tool. The sampling pressure remains quite con­ stant until the tester is full (G), when it rises to the shut-in formation pressure. At I the seal valve is closed and is followed at J by the retraction of the tool. Since the sample line pressure does not rise to the hydrostatic pressure of the mud column, it is obvious the pad i, TEST RECORD still stuck against the wall of the hole. The get-away MECHANICAL FLOW LINE PRESSURE tJ ACIlOJ 4 ·m,PS' shots are, therefore, fired at K and the increase hydrostatic mud pressure at L verifies that the tool is free and can be removed from the hole. 0 The results of this actual test, as indicated on the log, are as follows: formation shut-in pressure 5,000 psi; hydrostatic mud pressure, 7,200 psi; oil recovery, ~ULLET 1,500 cc; gas recovery, 3.9 cu ft; mud filtrate, 2,000 ~s~ 0 ffl TESTER OPEN cc; sand, 50 cc; and gas-oil ratio, 414: 1. A subsequent OIl". production test in the formation, a thin-sand section of 0 SAMPLING PRESSURE 6 ft, recovered 244 bbl of 34.6 gravity oil with no _4600 PSI water, and a GOR of 848.1.

The surface equipment includes a separator and Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 FILLUP TIME 0 laboratory-type gas meter. Samples of gas and liquids 112 37ltc. are preserved for laboratory analysis (Fig. 4). olin. ~TESTER FULL ANALYSIS OF FIELD RESULTS SHUT-IN PRESSURE The formation tester has been used commercially in 1--&000 PSI the Gulf Coasts of Louisiana and Texas since July, I H min. 1955. The results obtained in the first 1,000 runs (Sept. - 1, 1956) have proven the practicability of the method. rB-VALVE ~ The results give a 50 per cent successful operation ratio. ICLOSED - About 10 per cent of the failures have been successful 'TOOL when rerun. A positive interpretation has been possible RETRACTS in most of the recoveries, but there are some cases in It which interpretation is impossible, or, at best, doubtful. r----B- Min. As in the operation of most down-hole logging or test­ ing devices, the border line formations give the most trouble. Further, it can be said that, due to its ready applicability, this tool has been run on more question­

2 able sands than on good sands. 1IIIn. It should also be pointed out that 50 per cent of 0 the failures were due to ineffective pad seals in very GET-AWAY soft Miocene sands. It is believed that testing of those SHOT .J ,/0 sands will be done with a percussion-type fluid sam­ .... TESTER FREE I pler. (This tool is capable of recovering five samples I per trip in the hole. Each sample is selectively shot •• HYDROS1lITIC HEAD 1-7200 PSI The fluid sampler does not require a seal pad, as the

FIG. 3-LOG OF A FORMATION TEST AT 11,000 FT. FROM LEFT TO RIGHT ARE REPRESENTED ClJRVES 1 AND 2. RESULT Of TEST Formation shut-in pressure: 5,000 psi Hydrostatic pressure of mud: 7,200 psi R"ecovered gas 3.9 cu ft; oil 1,500 CC; sand 50 CCi mud filtrate 2,000 cc Gas/Oil ratio of sample, 414/1 Production Test: perforated 6 ft of formation Recovered, 244 B/D, Gr. 34.6 GOR, 848/1 pad). Curve No. 2 is the electrical indicator for precise timing of pad and valve operations. The entire test can be followed by reading down this example. At the top of the example is the SP curve recorded as on the electrical log in order to place the tool accurately in the formation. When the depth setting has been made, the recording film is geared to a timing device so that the vertical scale is a measure of elapsed time. In the left track, the pad-expanding operation is indicated at A; the seal pad being set at B. At C the sample bullets are fired. In the right-hand track, the FIG. 4--FORMATION TESTER CHAMBER (A), GAS sample line pressure before the test is given at D. The SEPARATOR (B), AND GAS METER (C), FOR sharp rise at E, after opening the tool to the formation MEASURING THE SAMPLE.

PETROLEUM TRANSACTIONS, AIME 262 percussion bullet penetrates beyond the flushed zones porosity and permeability. This problem can be partially while connected to a 330-cc chamber through a hollow minimized by a better control of the water loss in the tube. After a short time period, the tool is pulled up­ mud and by the use of the now available 2.75- and ward. This movement automatically seals the sample 5.5-gal reservoirs. The formation pressure can be useful. in the reservoir.) THE RECOVERY IS ONLY A FEW CC OF FILTRATE Running the gauntlet of successes and failures, the AND A SMALL AMOUNT OF GAS formation tester has recovered a full reservoir of pipe­ line oil, a full reservoir of dry gas, a fulI reservoir of This must be considered a dry test. Such a test can formation water, a full reservoir of mud filtrate, and be obtained from an oil-sand if it is attempted in a a full reservoir of formation fluids contaminated with shaly or impervious streak. If the sand appears good mud or mud filtrate. It has also recovered partial sam­ on the electric log, another test in the same sand ples of one or several of the above fluids and, on some should be attempted. From limited experience, it is be­ occasions, nothing at all. In evaulating such results, it lieved that a second dry test in a thin sand, 10 ft or is well to point out the value of maintaining a low water­ less, is a good indication that no commercial produc­ loss mud in order to better limit the amount of filtrate tion can be expected without special treatment. contamination of the sample. The use of the 2.75- or THE RECOVERY IS MUD ONLY 5.5-gal reservoirs also insures obtaining a more repre­ This is a misrun. In soft, unconsolidated formations, sentative test. The larger reservoirs give a reduction in many failures are caused by the sand actually flowing proportion of filtrate recovery and the increased volume into the testing tool. Irregularities of the face of the enables more positive interpretation. borehole can also cause failure of the seal pad. Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 One major company has had 41 successful tests out of 80 attempts, with 23 ineffective pad seals. Results THE PRESSURE CHART for this company were highly satisfactory in pinpoint­ ing gas-oil ratios, indicating productive permeabilities. The recording of the pressure build-up curve at the and aiding in determinations of fluid content where surface has obvious advantages: the electrical log and side-wall core interpretation was 1. It gives the engineer visual control of the tool inconclusive. during the testing operation. A seal pad failure, or a lack of pressure build-up is known almost immediately. A DISCUSSION OF THE RECOVERIES Likewise, the characteristic curve of a successful test is promptly recognized. The fluid recoveries obtained to date can be classified 2. It furnishes a permanent record of the testing in six main categories. These categories are listed to­ operation. gether with an interpretation based on field experience. 3. It measures both formation pressure and mud THE RECOVERY IS SUBSTANTIALLY OIL pressure at the depth of the test. The pressure gauge AND GAS WITH SOME FILTRATE presently incorporated in the tester has good accuracy, ± 3 per cent. Formation pressures can thus be rea­ This formation will probably produce oil and ga~ sonably determined. Pressure measurement technique with no water. A very close estimate of the GOR can will be improved in the near future to accomplish an be predicted. The gravity and type of oil can be es­ accuracy of 1 per cent. tablished. The formation pressure, always a very im­ portant factor, is established. As field experience was gained with the formation tester, it became apparent that the pressure chart was THE RECOVERY IS SUBSTANTIALLY SALT WATER the key to certain formational characteristics. A thor­ WITH A MINIMUM AMOUNT OF GAS, ough study of the results thus far obtained indicates USUALLY ABOUT 1/10 CU FT that the charts fall into a family of eight basic cate­ This formation will, no doubt, produce salt water. gories. An idealized chart has been drawn for each The formation pressure is measured. category (see Figs. 5 and 6). A discussion of these characteristic charts will give a better understanding of THE RECOVERY OF OIL, AND/OR GAS, AND SALT WATER the performance of the tester under varying conditions Experience with this type of test is limited. The and the degree of formation analysis possible in each formation may produce all three fluids; on the other case. The typical range of elapsed time is indicated hand, it may produce only water. If possible, the well should be completed above the depth of the test. If this TOOL SET Lbs·O cannot be done, a completion at the sample depth may 2500 /5000 0 /2500 5000 0 2500 \ 5000 0 \ 2500 5000 be economical if the water-cut is not too high. With additional experience, it may be possible to predict the .0 min. percentages of fluids that will be produced from the percentage of each recovered in the sample. The form­ ation pressure is of interest.

THE RECOVERY IS ONLY MUD FILTRATE

Strictly speaking, the only information obtained in 2,' SEAL 3C7' VAL( E ,'"d CLOSED 0"0 ~ this case is the formation pressure and the fact that min GET! "AWAY, ~~~~s FI~ED the formation is permeable. However, from the limited 3-.5 _ 4·8 10-1 '0.1'.,....,;,,;,...... experience to date, it is believed that, if a formation is MUD P~ESSUREl MUD PRksSUREI MUD PRkS9UR~ MUD PRksSUREI I I I I to be productive, there should be at least a trace of oil and some gas present in a test. There are exceptions I. IDEAL TEST 2. LOW FLOW- 3.FORMATION 4,DRY TEST ING PRESSURE PRESSURE to most rules, and there may be exceptions to this one. ONLY Of course, deep invasion usually indicates relatively low FIG. 5-PRESSURE CHART INTERPRETATION.

263 VOl•. 210, 1957 TOOL SET sampling pressure, formation pressure, and hydrostatic Lb. 2500 / 5000 o 2500 75000 0 \ 2500 5000 0 \ 2500 5000 mud pressure are all part of a permanent original rec­ '0 I 1 TEST STARTS ord on film. In addition, the indications of the sequence o _L.l o~ .- of tool operations on the film provide better control and ml n oH:...- 07-1-- later verification of the test procedure. PROBABLE ~~E'i SAMPLING I SAMPLING A-( -PRESSURE The method provides extreme accuracy in depth con­ PRESSURE I trol through coupling the setting depth to a simultaneous I [ -B recording of the SP curve which may be correlated I I I !::b with the electric log. The accuracy of depth setting is SEAL VALVE CLOSED PRESSURE 2' 5'·rJ -So considered to be ± 6 in. n· The system is actually a pinpoint fluid-sampling op­ GEt AW4y GJN [ 3' 11·9' 4'·8' FIR~D eration. At the very most, only a few inches of forma­ ml n, MUD PRESSURE MUD PRESSURE MUD PRESSURE MUD PRESSURE tion are sampled on anyone test. By successive tests. I I I complete production profiles can be made, giving very 5. MISSRUN 6. MISSRUN 7. A.PARTIAL B. HIGH VISCOS· accurately the thickness of the producible formation, NO SEAL SEAL FAILURE PLUGGING ITY OIL the gas-oil, and the oil-water contacts. B.TOTAL PLUGGING Analysis of the recovery on the surface enables the FIG. 6-----PRESSGRE CHART INTERPRETATION. determination of type of fluid and gravity of the oil. Samples of the gas can be analyzed by the hot-wire at the left of each chart. Testing time starts when method for indication of the hydrocarbons present. The Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 the bullets are fired. gas-oil ratio can be calculated. Though this ratio is Chart No.1: This type of pressure curve is obtained the minimum gas-oil ratio, and not necessarily the pro­ from a highly permeable formation. duction ratio, field results indicate that it is close to Chart No.2: This type of pressure curve is obtained the initial gas-oil ratio encountered on completion. from a formation with a somewhat lower permeability Laboratory analysis of the sample may be made to than that of Chart No. 1. This is indicated by the determine the marketability of the producible products lower sampling pressure and a slightly longer testing before a decision on the type of completion is made. time. Analysis and measurement of resistivities of aqueous Chart No.3: This pressure recording is obtained from solutions in the sample can be made to increase knowl­ a formation with very low permeability. The flow was edge of the nature of the reservoir and aid in the in­ insufficient to indicate a pressure in the sample con­ terpretation of logs obtained in other wells in the area. tainer; however, it was possible to obtain the forma­ Safe testing is assured by this cable-operated device. tion pressure in the flow line. The formation pressure is contained by the full mud Chart No.4: This illustrates the type of chart ob­ column during the entire operation. This makes the tained from formations with extremely low permeabil­ system practicable for deep high-pressure wells in which ity. The flow was too small to indicate a pressure in the risks involved have made the setting of casing either the sample container or the flow line. mandatory for the utilization of normal testing methods. Chart No.5: In this test, the pressure curve shows Other safety and economic benefits are achieved clearly that a seal was not affected; therefore, this is through the foreknowledge of formation pressures to a misrun. be encountered in the well completion and prior to ad­ Chart No.6: The pressure curve here indicates that ditional drilling in an area. These include savings in the seal was obtained but failed before completion of mud and equipment costs and the correct selection of the test. control equipment for handling high pressures. Chart No.7: This is an example of plugging of the flow line before completion of the sampling. Point FIELD EXAMPLES A indicates partial plugging. Point B indicates total plugging, making it impossible to obtain the formation (The following discussions are based on actual field pressure. If only partial plugging occurs, formation examples which well illustrate successful operations in pressure can be obtained. severai areas of the Gulf Coast) Chart No.8: This chart is similar to No.2. In this EXAMPLE No.1 (FIG. 7) case, the high viscosity of the oil contributes to a low sampling pressure and a slightly longer testing time. One of the most difficult problems on the Gulf Coast, This is caused by the low relative permeability of this both in logging and, to a lesser extent, in core analysis, sand to the viscous fluid. is the differentiation between oil- and gas-bearing forma­ tions. The difficulty is increased when the sands are un· ADVANTAGES OFFERED BY THE METHOD consolidated and the gravity of the oil is greater tha:l 40 API. Several advantages of this method of formation test­ The electrical log and MicroLog covering a sand in ing by a tool operating on logging cable can be noted. the second well of a new field are shown in Fig. 7, Inherent in the system is the time-saving character­ Analysis of side-wall cores in this same sand in the dis­ istic of wire-line tools. One test can be made safely at covery well indicated zero oil saturation at the equivalent 10,000 ft in two hours. This is total trip; time running depth of 9,300 ft. Three side-wall cores below 9,300 ft in, test time, and pulling out. gave an oil saturation varying from 2 to 6.3 per cent. The testing can be done immediately following the It was concluded on the basis of these cores that the electrical log or at any time during the drilling opera­ sand was gas bearing and, therefore, the well was com­ tions. No special well conditioning such as ratholing is pleted in another horizon. required. Core analysis of the section in the second well, shown As in most other logging tools, the complete cycle here, gave an average oil saturation of only 6 per cent; of the tool operation is recorded at the surface. The however, at 9,294 ft the formation tester gave 1.75

PETROLEUM TRANSACTIONS, AIME 264 pints of oil, 7.5 cu ft of gas, and 3 pints of filtrate. The black oil recovered further contributed to a non-com­ calculated GOR from this test was 1,440, with a flowing mercial evaluation of the reservoir. Nevertheless, an pressure of 4,300 psi and a shut-in pressure of 4,400 open hole drill-stem test of the entire sand body was psi. At 9,290 ft, a second test, 4 ft above the first one, made; it recovered 9.4 bbl of salty gas cut mud and gave a GOR of 3,494. 9.7 bbl of slightly oily salt water, with a flowing pres­ It was then concluded that an oil completion should sure of 825 psi. The well was abandoned. be made. After perforating from 9,296 to 9,300 ft, the EXAMPLE No.4 (FIG. 10) well produced 211 bbl of oil with a normal gas-oil ratio of 1,284, a FFBHP of 4,275, and a SIP of 4,375. The Conventional diamond coring of the sand A in this excellent correspondence of the pressures given by the example revealed a definite oil saturation. The core formation tester and the pressures obtained on the final analysis gave the following average values: porosity, production test, was very encouraging. It should be 29.6 per cent; permeability, 507 md; gas by volume, noted that successive measurements of GOR on the 8.8 per cent: water saturation, 65.6 per cent; oil satura- same test, when made by methods now in common prac­ tice, will vary by 200 cu ft/bbl. It was later established ELECTRICAL LOG MICROLOG CORE that the upper formation test, giving a GOR of 3,494, ANALYSIS had been taken at the exact gas-oil contact of the field. 'Yo Oil SAT ,0 ~ In this example, the formation tester contributed to the discovery of a new oil pay and gave accurate GOR

figures. Since completion of this well, the formation Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 tester has been used to evaluate several other sands in the same field, and it is believed that each sample has been as valuable as a casing drill-stem test in planning the development of the field. EXAMPLE No.2 (FIG. 8) Electrical logs and cores in this South Louisiana wdl ISERVILLE PH., LA indicated two saturated sands of low porosity and per­ FIG. 7-FoRMATION TESTER DISCOVERS AN OIL SAND. Formation Test No. 1 at 9,29.4 ft: Recovered 13/4 pints oil; 7.5 cu ft gas; meability. The company decided to use the formation 3 pints filtrate and sand; GOR 1,440; FP 4,300 Ib; SIP 4,400 Ib tester. The six tests shown in Fig. 8 were all dry, indi­ Formation Test No. 2 at 9,290 ft: Recovered 1 pint oil; 10.4 cu ft gas; 1 pint sand; 4 pints filtrate; GOR 3,494; FP 4,300 Ib; SIP 4,400 Ib cating the horizons to be nonproductive. Not satisfied Drill·stem Test (GP 9,296 to 9,300 ft, Open 5% hours, TP 1,980 Ib; with these results, the company decided to sidetrack flowed 211 bbl oil; '/.-in. choke; GOR 1,284; FFBHP 4,375 Ib the well a few feet to diamond core and analyze the ELECTRICAL LOG sands. The upper sand gave an average porosity of 16 MICROLOG 16' SN per cent and average permeability of 1.6 md (maxi­ j)~"-.J..rL AMP SN mum 4.2). The lower sand gave 17.2 per cent porosity o 5 and 1.5 md (maximum 2.7). The well was plugged. The formation tester had indicated that both sands were nonproductive. Moreover, a close analysis of the electrical log and the MicroLog gave estimates of water saturations between 50 and 55 per cent, and permeabil­ ities below 25 md. 9 7/8" HOLE With more experience, substantiating evidence of this ALL 6 Rm = 0.25 BHT type will undoubtedly be accepted as sufficient to evalu­ FORM TESTS ate the formation as non-commercial. Costly sidetracks, f-----~---1 DRY or other methods of obtaining additional information will often be eliminated. Thus dry tests, as made in this well, offer valuable information. It is recommended, in cases of low perme­ ability such as this one or in cases where the sand is known to be shaly, that more than one test be made FIG. 8-FoRMATION TESTING IN Low PERMEABILITY SANDS. to assure a fair evaluation of the zone. ELECTRICAL LOG MICROLOG EXAMPLE No.3 (FIG. 9)

This electrical log and MicroLog, in the "hard rock" 20 country of Central Mississippi, indicated a potential pro­ ductive sand in the Glen Rose. Side-wall core analysis gave porosities of 19 to 29 per cent with oil saturations of 5 to 20 per cent. Two formation tests were made at 8,421 ft, each recovering traces of oil and 3.8 quarts of filtrate. Flowing pressures in the two tests were 600 and 500 psi; shut-in pressures were identical at 3,800 lb. YAZOO CO ,MISS A third formation test at 8,405 ft recovered 1 FIG. 9-FoRMATION TESTS IN "HARD ROCK" COUNTRY OF quart of filtrate, with 500 psi flowing pressure, and 3,700 CENTRAL MISSISSIPPI. formation Test No. 1 at 8,421 ft: Recovered 3.8 quarts filtrate, trace oil, psi shut-in pressure. FP 600 Ib; SIP 3,800 Ib Formation Test No. 2 at 8,421 ft: Recovered 3.8 quarts filtrate, trace oil, The recoveries of filtrate indicated extreme invasion, FP 500 lb.; SIP 3,BOO Ib which explained, partially, the high resistivities on the Formation Test No. 3 at 8,405 ft: Recovered 1 quart filtrate, FP 500 Ib; SIP 3,700 Ib electrical log. The very low flowing pressures were also Drill-stem Test (8,397 to 8,454 It), Open 25 minutes, pressure % Ib, recovered 9.4 bbl salty gas cut mud and 9.7 bbl. gassy, slightly oily, indicative of extremely low permeabilities. The traces of salt water (16) FFP 825

265 VOL. 210, 1957 CALIPER ELECTRICAL LOG MICROLOG THE COMPARISON ~ ~P ______~IO~ p 5, BIT o Z 5 ~ SIZE FLOWllHi PRESSURE

SHlH-IN PRESSURE

I

lOOL OPO' FOR lllllH,3ASEC

21.CO FTGAS

<,zee OISTILlAT( 29'OISllU.l.TE

.'nCCFtLTRAT( TRACE OF MUO

RESISTIVITY OFTHE Z35,\f67oF 8ITSll[ 7'. """26 .. '61*,

FIG. 12-COMPARISON OF FORMATION TESTER RESULTS WITH THOSE OF DST OVER SAME INTERVAL.

CORE ANALYSIS (Al FORMATION TEST REC. RESISTIVITY MICROLOG POR.: 21 % SP 2835 SW PERM.: 500 MV cc (170000 PP M ) OIL: 5 % 9 5/8" HOLE 4 72 cc SAND MICRO-CAliPER - ~ + NORMALS LATERAL V!TR.: 65% Rm s 0.25 BHT 8 910" , , I 10 0 2 0 2 3 FIG. lO-FoRMATION TESTER CONFIRMS QUANTITATlVF: ANAl.YSIS

OF El.ECTRICAL LOGs. Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021

s. P. RESISTIVITY <;> AM:16" a AM'=64" 20 -~+ o AMP. NORM.=16" 4,QLAJ-

2 FORMATION TEST .. 1- 1.2cuft. TESTS AT GAS 2800cc 3573' _ FILTRATE

Rm: 1.8 at 86°F. HOLE. 83/4" TEST #2 - 3cu.ft. GAS 2000 cc FIG. 13-FoRMATION TESTER INCLUDED IN DRILLING PROGRAM. FILTRATE Recovery of Formation Tester: 22.2 cu ft gas, 75 cc distillate, 200 cc filtrate, sampling pressure 2,900 psi, shut-in pressure 3,000 psi PROD. TEST- Drill-stem Test: 51 MMcf gas and 27 bbl distillate per MMcf gas-Flowing 1000 MCF OF GAS Pressure 2,860 psi ON 24/64"CHOKE Formation Test No.1 at 8,818 ft: Recovered 0.07 cu ft gas .. 100 cc mud­ FLOWING PRESS: cake, shut-in pressure 200 Ib, HMP 4,500 Ib 400 PSI HOLE SIZE: 97/8' EXAMPLE No.6 (FIG. 12) MUD RES. : 1.00 AT 98° F. This is an actual comparison of a standard open hole FIG. ll-FoRMATION TESTING OF THIN PAY IN SOUTH TEXAS. drill-stem test and a formation tester operation over the same interval. tion, 5.2 per cent. Quantitave analysis of the electrical A very close similarity exists between the two tests, log, however, pronounced the zone a water-bearing sand. particularly in the pressures obtained. For confirmation, a formation test was requested. It is obvious the filtrate recovered by the formation The tester recovered 0.2 cu ft of gas and 2,835 cc of tester was uncontaminated by any formation water. salt water. The resistivity of the recovered water was Calculations of the connate water resistivity indicate 0.04 ohm (170,000 ppm NaCL equivalent). Compari­ 0.06 ohm at BHT, while the resistivity of the recovered son with the mud filtrate resistivity of 0.6 ohm easily filtrate is almost equal to the resistivity of the mud. established that the recovery was formation water, and EXAMPLE No.7 (FIG. 13) not mud filtrate. The well was immediately plugged, The use of the formation tester was included in the thus saving a long string of casing and expensive testing. drilling program for this well. A mud-logging unit re­ EXAMPLE No.5 (FIG. 11) ported a gas show at 7,460 ft. After running the elec­ The electrical log in this South Texas well indicates trical log at a TD of 8,500 ft, the formation tester, a thin potential pay from 3,571 to 3,575 ft in a shaly set at 7,462 ft, recovered 22.2 cu ft of gas; 75 cc of sand. Wire-line cores were analyzed with the following distillate, and 200 cc of filtrate. Sampling pressure was results: porosity, 28 per cent; permeability, 525 md; 2,900 lb; shut-in pressure was 3,000 lb. Side-wall cores residual oil saturation, 15 per cent (gravity above 42 had a few shaly laminations; thus, an average perme­ API); residual water saturation, 47.5 per cent. An oil ability of only 50 md was measured. This was ques­ well was predicted. tioned, in view of the excellent results of the formation tester. Larger side-wall cores gave 300 to 400 md, but However, the formation tester run twice at 3,573 ft core analysis had difficulty in predicting hydrocarbon produced only 1.2 and 3 cu ft of gas together with con­ saturations; the low-water saturation, however, was very siderable filtrate. The sampling pressures were 500 and encouraging. 900 psi. The shut-in pressures were 1,100 psi. The drill-stem test, after perforating from 7,458 to Due to the fact that no trace of oil was found in 7,464 ft gave a shut-in pressure on the tubing of 2,860 the recovered samples, it was decided that this was a lb, using a 1;4-in. choke on bottom and a 6/64-in. choke gas sand. on the top. Identical flowing pressure of 2,860 lb was Testing through casing resulted in 1,000 Met on measured on the tUbing. 24/64-in. choke, with a 400 psi flowing pressure. There The final closed-in pressure was 3,394 lb. The well was no oil produced. produced 51 MMcf of gas, with 27 bbl of distillate

PETROLElJM TRANSACTIONS, AIME 266 RESISTIVIT) per MMcf (gravity, 57.6). The GOR was 36.65 S. p. Mcf/bbl. -ohms. m2/m AM'16"' Ii AM-64"

EXAMPLE No.8 (FIG. 14) AMP. NORMAL AM 0 IS" High invasion is evident by the large separation of TEST#I- WITH 5GAL the resistivity curves. The very low reading on the TESTER RECQVERY-144ct GAS lateral curve is due to the anisotropy of the shale above 315 cc OIL 7,350 ft. Standard quantitative evaluation of the elec­ 775ccMUD tric log would have condemned the sand. In this test G P : the 5.5-gal reservoir was used. Due to the high invasion the I-gal tester would probably have recovered only filtrate. CONCLUSIONS

~ ne formation tester operating on logging cable has TOTAL DEPTH: 8300' been introduced. It offers all the advantages of speed, HOLE SIZE: e 3/4" MUD RES.: 1 4 at 96 D F safety and versatility characteristic of wire-line opera­ FIG. 14--FIVE-GALLON TESTER SOLVES A DIFFICULT PROBLEM. tions. Experience to date on over 1,000 operations has been largely confined to unconsolidated sand and shale Since the method includes only a small volume of formations. Interpretable results on over 50 per cent Downloaded from http://onepetro.org/trans/article-pdf/210/01/260/2176739/spe-701-g.pdf by guest on 26 September 2021 formation in each test, a series of several tests within of these operations indicate a performance which jus­ a single zone will establish permeability changes, oil­ tifies continued and expanded development. water and gas-oil contacts. The tool is an important adjunct to electrical log­ Reservoir analysis, using data obtained with the ging and side-wall coring operations. It offers an ac­ formation tester, will, no doubt, increase in scope with curate and economical method for testing formations increased application of the tool and with further im­ pen~trated by the drill without conventional coring and provement in design. Already, the pressure measure­ test.mg Becaus~ .. the full hydrostatic mud pressure is ments are being used to determine more accurately the mamtaI.ned dunng the entire operation, it can be used compressibility factor, viscosity, and solubility. Improve­ safely m deep high pressure wells. Bottom-hole pres­ ment in the accuracy of the pressure measurement will sure and mud pressure are recorded at the surface. increase its value in reservoir studies as, for example, Tools with reservoir capacities of 1, 2.75, and 5.5 gal the study of hydraulic gradients'. are being produced. Ex~mination and analysis of the recovered samples PVT analysis will be simplified by recovery of fluid estabhsh~s or confir~ns the presence of oil or gas in the before the formation has been allowed to produce, and prospectIve productIOn zone. Gravity of the oil and under controlled conditions. gas-oil rat!os may be determined. Laboratory analysis It is anticipated also that quantitative studies of of recovenes may affect economic considerations related permeability and productivity index based on formation to completion of the well, particularly where a choice tester data may become possible. of several production zones is possible. Interpretation of pressure recordings obtained at the REFERENCE surface during the tests gives added valuable infor­ 1. "Entrapment of Petroleum Under Hydrodynamie Condi- mation on the permeability of the tested zones. tions," Bull. AAPG, 17, No. H. ***

267 ,VOl•. 2]0, 1957