In-Situ Stress Research Articles

Overview: Multilateral/Extended Reach (July 2005)

Ret-ro-spec-tion (n): the act or process of surveying the past. What does retrospection have to do with multilateral (ML) and extended reach (ER) wells? By the time this issue of JPT is published, I will have retired from 31 years of active duty in the oil patch. Reaching this milestone made me think about the past and the advances in drilling technology and practices. Approximately 25 years ago, directional drilling was used predominantly to develop reserves, mostly offshore, that could not be accessed any other way. Around 1980, horizontal wells changed that mindset and directional drilling became a reservoir-management tool. The idea of horizontal wells or drain holes was not new; successful applications of the technique were reported as early as 1929.1 Instead of discussing why horizontal wells took 50 years to catch on, let us look at some key well-construction technologies that made it a reality. By the late 1980s, several technologies—measurement while drilling, steerable motors, top drives, and polycrystalline diamond compact bits2—combined to increase drilling efficiency and reduce drilling and reservoir risk. When first introduced, these technologies were sold as time savers—through connections, surveys, trips, or increased rate of penetration. We know these efficiencies are tangible, but the real value is the drilling system that made horizontal wells an effective reservoir-development tool. The industry first considered ER technology in the early 1980s to access reserves beyond the original development area from offshore platforms—many of these developments were based on pre-1980s directional-drilling limits of 60°. In these cases, ER wells were more cost-effective than a second platform or subsea completions. However, it was not long before ER wells became an option in the development of offshore reserves from an onshore pad or the basis of a new development plan. The one-trip retrievable whipstock is considered an enabling technology for MLs. Introduced in the early 1990s, it was considered a timesaving tool. But when combined with Technology Advancement of Multilaterals Level 1, 2, or 3 junctions, this technology resulted in the economical development of several heavy-oil projects. Once again, the real value was in effectiveness, not efficiency. World-class wells of 10 years ago are considered routine today. What will a world-class well look like 10 years from now? I cannot answer that question. But I am confident that value-adding technologies will be those that break current paradigms, not those that enable us to do things faster or cheaper. I will be watching these pages for the answer.

The Recent State of Stress in the Central Qinghai-Tibet Plateau according to In-Situ Stress Measurements

The Qinghai-Tibet plateau is the most active in tectonic activity. In order to learn the recent state of stress, we have carried out stress measurements at different structural positions and depths and in different rocks by using piezomagnetic stress gauge overcoring method in the central Qinghai-Tibet plateau. The results of stress measurements indicate that the direction of the maximum principal stress is generally in NE direction. This agrees with the result of the studies of geology, seismology, and geodesy. The values of the maximum principal stress are 3.6-6.8MPa which are medium or slightly high compared with those obtained elsewhere in China from a viewpoint of regional stress analysis. But the stress measurement site at Amdo is an exception where the direction of the maximum principal stress is NWW and its value is 8.1MPa. This also indicates that the recent state of stress is complex near the plate suture zone. These results of stress measurements can provide important basic data for studies of active faults, geological hazards and engineering stability evaluation in the Qinghai-Tibet railway construction area as well as for research of continental dynamics.

In-Situ Stress Measurements During Aluminum Deposition from AlCl3-EtMeImCl

In-Situ Stress Measurements During Aluminum Deposition from AlCl3-EtMeImCl

In-Situ Stress Investigation of Jingqiu Oil Field Sand Section No. 2 Oil-Bottom Structure

In-Situ Stress Investigation of Jingqiu Oil Field Sand Section No. 2 Oil-Bottom Structure

In-Situ Stress Measurements in the Preexcavation Design Stage of the Serra Da Mesa Hydroelectric Project, Brazil

In-Situ Stress Measurements in the Preexcavation Design Stage of the Serra Da Mesa Hydroelectric Project, Brazil

In-Situ Stress Measurements During Dry Oxidation of Silicon

ABSTRACTIn this study, we present results of both in-situ and ex-situ measurements of stress generated during dry oxidation of silicon. We show that the mechanical stress in as-grown dry oxides is a strong function of oxidation temperature and oxide thickness, but a weak function of oxygen partial pressure. We have identified a structural relaxation phenomenon after the oxide is formed, and found that the viscosity of the oxide increases with its age; consequently, the stress relaxation slows down due to this increase of viscosity. In this paper, we present a one-dimensional mechanical model to simulate the stress generation and relaxation during dry oxidation of silicon. The simulations of both in-situ and ex-situ tests are in good agreement with the experimental measurements.

In-Situ Stress and Rock Strength in the GBRN/DOE Pathfinder Well, South Eugene Island, Gulf of Mexico

The authors present a relatively simple technique to constrain in-situ stress and effective rock strength from observations of wellbore failure in inclined wells. Application of this technique in the Global Basins Research Network (GBRN)/DOE Pathfinder well demonstrated that (1) the azimuth of S{sub h min} is {approx} N42{degree}E, perpendicular to a major growth fault penetrated by the well; (2) the magnitude of S{sub H max} is relatively close to the vertical stress; and (3) the effective in-situ compressive rock strength is 3,500 to 4,000 psi. They show that once they have estimated in-situ stress and rock strength, it is possible to compute the mud pressure required to inhibit failure for wells of any azimuth and inclination. Finally, they show how it is possible to estimate the magnitudes of both S{sub h min} and S{sub H max} in cases where independent knowledge of stress orientation is available (for example, from wellbore breakouts in nearby vertical boreholes).

In-Situ Stress Profiling and Prediction of Hydraulic Fracture Azimuth for the West Texas Canyon Sands Formation

Summary This paper presents results of hydraulic fracture azimuth and in-situ stress measurements for two wells in the west Texas Canyon Sands formation. The paper gives information for designing infill drilling patterns and improving fracture treatment designs. Eight techniques were applied to measure fracture azimuth; the results from each are discussed. In-situ stress was measured in 12 intervals, and the results were used to calibrate long-spaced digital sonic logs. This paper also discusses the application of calibrated stress to fracture treatment design.

In-Situ Stress Tests and Acoustic Logs Determine Mechanical Properties and Stress Profiles in the Devonian Shales

SummaryThe in-situ stress contrast between a reservoir rock and the surrounding formations is important to the design and analysis of hydraulic fracture treatments. The stress contrast between layers controls the fracture's vertical (height) growth, which in turn affects the fracture length and width. As part of the Gas Research Inst.'s (GRI's) Comprehensive Study Well (CSW) program in the Devonian shales of the Appalachian basin, we measured in-situ stresses directly and used these values to calibrate acoustic log measurements to develop stress profiles across the Devonian shales. This discusses the measurement and interpretation of in-situ stresses, the use of acoustic logs to determine mechanical properties and a more complete stress profile, and the practical use of the stress profile in fracture-treatment design and analysis.In-situ stresses were measured directly throughout the Devonian shale interval with both openhole and cased-hole stress tests, conducted with nitrogen, a specially designed downhole shut-in tool, and a downhole quartz pressure gauge with surface readout. The paper describes the procedure used and presents interpreted stress-test results from two CSW's. Full-waveform acoustic tools were run to define elastic properties of the Devonian shales. These properties also were determined under both static and dynamic conditions from whole-core plugs taken in the shales. Logs were calibrated to core-measured values, and then elastic properties determined from the logs were used to compute an in-situ-stress profile, which was calibrated against field measurements of in-situ stresses. Finally, we discuss how these data are used to design and analyze hydraulic fracture treatments in CSW's.

In-Situ Stress Measurement - Results of Experiments Performed at the Asse Salt Mine - Federal Republic of Germany

ABSTRACTHigh-level nuclear wastes are heat generating wastes. Heat will be transferred to the surrounding salt formation. This heating of the host rock will result in an increased temperature and in stress changes.From 1983 through 1985 two underground tests were conducted in the Asse Salt Mine (Federal Republic of Germany) in which among others thermally induced stress changes were investigated.In the Temperature Test 6 which was conducted at the 750 m-level only electrical heaters were used to simulate the heat generating high-level waste. Three hydraulic stress monitoring stations were arranged in the un-heated area at a distance of about 40 meters to the central heater. Measurements using AWIO flat jacks were also carried out in the heated region of the Temperature Test Field 6 (TVF 6).The joint US/FRG Brine Migration Test (BMT) - a nuclear waste repository simulation experiment - was performed at the 800 m-level and used radioactive sources and electrical heaters to impose the heat load on the host rock. Stress change measurements during this experiment were performed using hydraulic pressure cells and straingaged stressmeters.During 1985 an experimental area for the first in-situ test disposal of high-level radioactive sources was created at the 800 m-level within the Asse anticline structure. Thirty high-level radioactive canisters will be emplaced in six down-boreholes located in two test galleries in the experimental area. There is one additional borehole in each gallery equipped only with electrical heaters. Hydraulic pressure cells, AWID flat jacks, and straingaged stressmeters were installed in the HAW-test field for stress change measurements.

In-Situ Stress Measurements During Drilling

Summary This paper describes the results of six microfracturing experiments in a gas well in south Texas. The experiments were conducted in open hole and during the drilling operations. Microfracturing consisted of pumping very small volumes of drilling mud (tens of gallons) at very low rates (3 to 30 gal/min [189 to 1892 X 10(-6) m3/s]). Three of these microfractures extended below the bottom of the open hole and were cored out. Created fracture orientation was obtained from the fractures observed in the oriented core. Several instantaneous shut-in pressures recorded in each zone showed variations of about 200 to 300 psi [1.4 to 2.1 MPa]. This magnitude change is attributable to heterogeneity of the rock. Measured values of instantaneous shut-in pressure (ISIP) did not show any trend with lithology (shale or sand-stone), mechanical properties, or tensile strength. properties, or tensile strength. Introduction The experimental work described in this paper answers two questions.In a given field, what is the orientation of induced hydraulic fractures?In a given field, is there enough stress contrast between adjacent zones for fracture containment? The method used is quite simple. Create a hydraulic fracture in the open hole while the well is being drilled. There is a good chance that the fracture will extend below the bottom of the hole. Core the bottom of the hole. Obtain fracture orientation by observing its direction in the oriented core. The advantages of this method of operation are that all the data are obtained very early in the life of the reservoir. Openhole fracturing eliminates the effects of casing and perforations on fracture orientation and pressure. Coring the fracture provides a very positive visual determination of fracture orientation. The petroleum literature contains many fine articles on the relationship between in-situ stresses and fracture height, the need for determining fracture orientation, and how such data can be used for optimizing reservoir performance. For the sake of brevity, this paper will not performance. For the sake of brevity, this paper will not include a literature survey or a discussion of why the experiments were conducted. The major emphasis will be on a more complete description of each operation and results. Veatch provides background information on hydraulic fracturing. Experimental Procedure All the experiments were conducted in a gas-producing well in south Texas. The well has two producing zones separated by shales. The experimental work consisted of creating microfractures in each producing zone and in the shale zones above, between, and below the zones. Oriented cores were also obtained from every fractured zone. These cores were tested for physical and mechanical properties as well as for determination of actual fracture properties as well as for determination of actual fracture orientation. The sequence of events for each microfracture was as follows.With the drillpipe out of the hole, the openhole packer was assembled. This assembly contained two Bourdon tube (BT) gauges that would record the fluid pressure in the drillpipe (tubing). The packer was attached to an anchor pipe. By changing the length of the anchor pipe, one can regulate how high above the hole bottom the packer will seat, thus regulating the height of the openhole section to be fractured.The packer was lowered into the hole with the drillpipe. Once on bottom, it was seated by application of a vertical force to the drillpipe.The surface lines between pumps and wellhead were pressurized to detect and repair any leaks. Next, the pressurized to detect and repair any leaks. Next, the drillpipe was pressurized to ensure proper seating of the openhole packer. A small pressure was also applied to the annulus to detect and repair any leaks.Microfracturing was done by pumping of drilling mud as the fracturing fluid. Specific details of microfracturing will be discussed later.After microfracturing, the packer was released and brought to the surface. BT gauges were recovered for later determination of actual bottomhole pressures (BHP's).An oriented core was cut from the bottom of the hole for physical and mechanical rock-property measurements, as well as for detection of fracture orientation. The following sections provide more detailed descriptions of some key operations. Wellbore Preparation. The hole was drilled and cased to a depth of 7,750 ft [2362 m] according to standard oilfield operations. P. 891

In-Situ Stress Measurements at U. S. DOE's Multiwell Experiment Site, Mesaverde Group, Rifle, Colorado

Summary Vertical distribution measurements of the minimumprincipal in-situ stress in the lower Mesaverde group principal in-situ stress in the lower Mesaverde group (7,300- to 8,100-ft [2225- to 2470-m] depth) at the U.S. DOE'sMultiwell Experiment (MWX) site have been made by conducting small-volume, hydraulic-fracture stress teststhrough perforations. Accurate, reproducible results wereobtained by conducting repeated injections in each zoneof interest with a specially designed pump system, modified high-resolution electronic equipment, and adownhole shut-off tool with a bottomhole pressure (BHP)transducer. Stress tests were conducted in marines and stones and shales as well as in coal, mudstone, andsandstone in a paludal depositional environment; these testsprovide a detailed stress distribution in this region. provide a detailed stress distribution in this region. The stress magnitudes were found to depend on lithology. Marine shales above and below the blanket sands have large horizontal stresses that are nearlylithostatic, with a fracture gradient greater than 1.0 psi/ft[23 kPa/m]. This indicates that these rocks do not behaveelastically and processes such as creep and possibly fracturing are the dominant mechanisms controlling the stressstate. Sandstones and siltstones have much lower stresses. with a fracture gradient of 0.85 to 0.9 psi/ft [19 to 20kPa/m]. Containment of hydraulic fractures would beexpected under these conditions. Only three data points wereobtained from the paludal interval; no significant stressdifferences were observed in the different lithologies. Introduction The vertical distribution of the minimum principalhorizontal in-situ stress, has a significant influenceon hydraulic fracture geometry. Perkins and Kern notedits importance with respect to fracture height, and Simonson et al demonstrated how to calculate fracture heightin a nonuniform, but symmetric, stress field. Laboratory and mineback experiments have provedthe effect of differences on fracture height, but, as yet, field experiments have not yielded conclusive results. This results primarily from the lack of detailedin-situ stress data and viable fracture height measurement techniques. In addition, few in-situ stress measurementshave been obtained in intervals where core is availableso that stress/rock-property correlations can be attempted. The present work on in-situ stress measurements is partof DOE's MWX program, which is being conducted inthe Piceance basin near Rifle, CO. In-situ stressmeasurements currently are planned throughout the entire4,000 ft [1200 m] of Mesaverde rocks encountered at thislocation, with particular emphasis on obtaining detailedstress measurements around formations to be stimulated. Over 4,000 ft [1200 m] of core have been obtained from three closely spaced wells (130 to 180 ft [40 to 65 m])so an abundance of core data is available. Complete conventional log suites, as well as various advanced and experimental logs including the long-space sonic logs, havebeen run. This paper presents the results of the initial series of in-situ stress tests, which were conducted at thebase of the Mesaverde in marine sandstones and shales and at various horizons in a paludal zone. These data willbe used to design hydraulic fracture treatments and aidin the analysis of postfracture performance. In-Situ Stress Measurements At present, the only reliable method of obtaining distribution is by measurement with small-volume hydraulic fractures. Two techniques are currently in use. The step-rate/flowback procedure, pioneered by Nolteand Smith, yields a reliable, reproducible estimate ofand typically is conducted in an interval soon tobe stimulated. These tests have been called "minifraes"because they use small volumes of fluid (500 to 10,000gal [2.0 to 40 M ]) compared with conventional fracture treatments. The technique used in this study also is calleda "minifrac, "although it uses much smaller pumped volumes (1 to 250 gal [0.004 to 1.0 m ]). Minifracsusually are conducted by injecting a small volume intothe formation, shutting in, and measuring the instantaneous shut-in pressure (ISIP). For openhole tests, several authors have discussed the technique'sdetails, and it is clear that when adequately conducted, the test yields an accurate, reproducible estimate ofand a somewhat less reliable estimate of the maximum horizontal in-situ stress,. For most oil and gas applications, however, it isimpossible or impractical to conduct these tests in anopenhole environment. Problems with hole stability, gaspressure, cementing, and cost factors usually require that pressure, cementing, and cost factors usually require that the tests be conducted in cased holes through perforations. This causes additional complications because of casing, cement annulus, explosive perforation damage, andrandom perforation orientation effects. JPT p. 527