Introduction to Cased-Hole Data Acquisition and Interpretation. Permanent Temperature Profiling

Transcription

1 Introduction to Cased-Hole Data Acquisition and Interpretation Permanent Temperature Profiling

2 Overview 1- Well Integrity Cementing: Cementing is a critical part of any well competition and subsequently well integrity. Poor cementing is responsible for casing outer wall corrosion, leaks and subsequently casing collapse. Corrosion: Corrosion is initiated immediately after placing the casing. The rate of corrosion depends on many factors such as casing metallurgy, poor cementing and casing stresses- to quote a few. Leaks: Leaks in casings and tubing will materialize in the long run. This again is a function of the metallurgy, cementing and borehole environment. 2- Production Logging: Water, oil and gas production from every zone. Productivity index and pressure for each zone Detection of leaks behind and inside casings Estimation of cross-flow between zones caused by uneven depletion. Three phase production in horizontal wells. 3- Reservoir Monitoring: Estimating fluid saturations of water, oil and gas behind conductive and nonconductive casings Applications of Pulsed neutron logging: capture mode (Σ) and Carbon/Oxygen mode. Resistivity (Rt) measurements behind conductive and non-conductive casings. Evaluating stand-alone PNL logs in old wells.

3 Permanent Sensors Well Integrity: Leak Detection/Temperature Profiling Annulus bleed-off Leak response Leak Detections- Temperature profiling: There are many forms of logging that are used to detect leaks (temperature, noise, oxygen activation, Injectivity). The most effective form is temperature profiling. The examples above show: Permanent Temperature sensors using fibre optics: This will become almost standard in the future where the temperature profiles continuously monitored. Standard E-Line temperature logging: The example on the right shows the geothermal logs for 20 wells. 3 of the wells show a deviation from the geothermal. An increase above geothermal means leak up behind the casing, and a decrease below the geothermal mean leak down ward.

4 Well Integrity: Corrosion Monitoring Corrosion Mechanisms: There are many corrosion mechanisms that take place downhole. These can be divided into 3 categories: Galvanic Chemical Mechanical (Stress) Five set of tools are used to quantify inner wall corrosion, outer wall corrosion, pits and cathodic protection design and evaluation.

5 Cathodic-Protection Log Electromagnetic Log Electric Log Well Integrity: Corrosion Monitoring Corrosion Monitoring and Protection: The example on the left shows a cathodic protection system evaluation giving the lowermost level of protection. The example on the right shows the combined log data from Cement, Electromagnetic and Electrical logging data. Note the perfect correlations between corrosion metal loss (middle tracks) with poor cementing (track on left) and electrical current leaving casing- anodic points (track on the right)

6 Well Integrity: Cementing Ultrasonic Rotating Flexural Wave The introduction of the ultrasonic rotating tool, followed by the rotating flexural wave measurement created a quantum jump in the quality of the cement evaluations. Ultrasonic: Measures the acoustic impedance of the cement Flexural wave: measure the compressive strength of the cement. The combination can define fluid (oil/water/gas) or solid (cement) circumferential coverage around the casing.

7 Spinner Calibrations Running the spinner at different velocities, in the opposite direction to the flow, provides the basis for spinner calibrations at any desired station, above perforations (B and C above) and at any station within the perforations (e.g. X). The slope of the straight line plot is the spinner sensitivity (velocity / rps which for a given spinner depends on the fluid type) and the intercept on the y-axis which is the rps due to the flow. The intercept on the x-axis represents the threshold, which is the frictional force, caused by mechanical and viscous friction, that represents the force needed to iniate the spinner response.

8 Water Production Coke: 2 1/8 Coke: 1 7/8 Water production is a serious production limiter in most fields. One common reason in high producers is water coning. Example shows how the water production drops by 80% without reducing (and often increasing) the oil production when the choke is decreased. A change in the choke from 2 1/8 to 1 7/8 reduced the top of the water entry level by 25 ft and increased the oil production by 700 bl/d.

9 Production Logging in Horizontal Wells Horizontal wells provide more challenges to production logging. Variations of velocities and hold-ups will span a wide range for little variations in flow volumes. This is caused mainly by small variations in the well trajectory around 90 degrees. New technology, like the FlowScanner Imager (FSI) are effective in evaluating multi-phase flow in horizontal wells.

10 Reservoir Monitoring Pulsed Neutron Logging Capture Mode Inelastic Mode Pulsed Neutron Logging (PNL) is the main tool that is used for reservoir monitoring. This involves two data acquisition types: Neutron Capture Mode (Σ). This is very effective where the water salinity is known.. Inelastic mode (Carbon/Oxygen). This relies.on spectroscopy and used mainly in where water salinity is unknown or the water salinity is very low.

11 Reservoir Monitoring PNL Life Cycle C/O Σ The minitron source fires around 20 million neutrons at speeds of 17 MeV. They interact (bump) into the various atoms, slow down, then they get captured. The whole life cycle of the neutron is approximately 200 m-sec (200 thousands of a second). The first 50 m-sec when the neutron are travelling fast is when spectroscopy takes place and C/O is obtained. The last 50 m-sec of the neutron cycle is when the capture mode slope is obtained.

12 Reservoir Monitoring PNL Capture Mode T0+6 T0+3 T0 for i n i 1 V. i i The Neutron Capture Mode (Σ) is the most practiced form of reservoir monitoring. It is very effective where the water salinity is high (>50 kppm). It is most applied form is time-lapse as shown above. The measured capture mode equation is the law of superposition as shown above where the measured Σ for is the integral sum of the fractional volume of each component multiplied by its unique Σ value.

13 Reservoir Monitoring PNL C/O Mode The Neutron High energy interaction can be used to obtain elemental evaluation of Carbon and Oxygen. Empirically derived trapeziums for C/O ratios of different detectors spaced at different distances can be used to obtain both values of Sw when the salinity is low or unknown and when combined with the capture Σ is also used to evaluate the fraction of the two waters sweeping across.

14 Introduction to Cased-Hole Data Acquisition and Interpretation This is a 3-day course which is an introduction to cased hole data acquisition and interpretations. The course covers three main cased hole topics: Well integrity: This covers corrosion mechanism and corrosion monitoring, leak detection and cement evaluation Production logging: This covers production logging in vertical, deviated and horizontal wells and also covers modern technology data acquisition tools to obtain holdups and velocities of the three phases: Water/oil/gas. Reservoir monitoring: This covers estimations of water and gas saturations behind conductive and non-conductive casings. This includes Pulsed Neutron (PNL) logging and resistivity logging behind conductive and non-conductive casings.. This class is open to all technical domains in the oil and gas industry. No prior cased hole experience is necessary. However, the course will also be beneficial to engineers with cased hole experience as it covers modern high technology tools' physics and operations. Agenda Day-1: Topic: Well Integrity Leak Detection using temperature and noise log profiling and oxygen activation to detect water movements inside and behind single and multiple casings. Corrosion Mechanism and Corrosion Monitoring. This covers new high technology corrosion monitoring tools and cathodic protection (CP) applications Cement Evaluation: New cement evaluations tools that give detailed circumferential coverage of cementing around the inner casing. Day-2: Topic: Production Logging The various high technology tools that are used to estimate the 3-fluid phase velocities The various high technology tools that are used to estimate the 3-vertical/deviated/horizontal wells. hold-ups. Production logging in vertical/deviated/horizontal wells. Day-3: Topic: Reservoir Monitoring Pulsed Neutron Logging (PNL): The physics and applications of PNL to estimate water saturation and gas saturation behind casings. PNL applications for gravel pack quality control and for log-inject-log applications. Cased Hole resistivity measurement behind conductive casings to obtain formation resistivity measurements.