Wireline Sand-Detection Tool Locates, Quantifies Downhole Sand Production
Field examples presented in the complete paper describe principles of data acquisition with a sand-detection tool when run in combination with a production logging string and results of logging in slightly deviated wells completed with sand screens.
Most of the wells in the Dzheitune (Lam) field in the Caspian Sea were completed with dual tubing. Depletion in reservoir pressure caused formation failure in the A sand reservoir, and wells producing from this formation began to produce sand. Field examples presented in the complete paper describe principles of data acquisition with a sand-detection tool when run in combination with a production logging string and results of logging in slightly deviated wells completed with sand screens. Comparison of multiphase-inflow profiles with sources of sand production showed that most sand was produced through eroded intervals in the sand screens.
Most Lam wells were completed with 9.625-in. casing and 7-in. liner across the reservoir section. The A sand reservoir, located at depths between approximately 1500 and 1800 m, and the CH sand reservoir, located below 2000 m, are produced separately by using dual-string tubing to avoid crossflow from the high-pressure CH reservoir into the low-pressure A reservoir.
When wells in the A reservoir began to produce sand, the operator had to change the completion strategy for newly drilled wells and had to recomplete some old wells by pulling out of hole dual-string completions and running in hole single tubing with sand screens across existing perforations. The top of sand accumulation in the annulus was identified with a slim sonic tool that measures cement-bond-log and variable-density-log data.
This change in completion strategy helped prevent sand production to the surface, but, eventually, several wells completed with sand screens across the A reservoir began to produce sand on the surface, damaging production facilities and plugging separators, which had to be cleaned periodically. To identify the source of sand production downhole and to verify the integrity of sand screens, a sand-detection tool was run on wireline in a few such wells.
Overview of the Wireline Sand-Detection Tool
The sand-detection tool, run on wireline, allows detection of sand-entry points downhole and determination of sand-production rates. The tool has a 360° detector element, as shown in Fig. 1, acoustically isolated from the rest of the tool housing by special elastomers. Thus, the wireline sand-detection tool is immune to background noise from tool motion, surface interference, and the effects of fluid and gas jetting. The detector element is very sensitive and can detect the impact of single sand particles as small as 0.1 mm in diameter and can measure up to 1,500 sand-grain impacts per second.
The digital downhole detection and processing system provides enhanced sensitivity for sand entry within a wellbore, allowing data acquisition while moving the tool across the logging interval. Once sand entry points are located, the detector element is placed across the sand-producing interval. Interpretation algorithms discriminate particles by their size and energy, apply smart thresholds, conduct a quality check of the count and detection rates, and determine sand-production rates with confidence.
The combination of the sand-detection tool and the production logging toolstring is conveyed downhole on wireline for real-time data acquisition as the well produces at one or multiple rates. During the logging job, data are acquired as the toolstring moves across logging interval at various speeds. Then, these data are analyzed for identification of producing intervals and location of sand-entry points. By use of these analysis results, depths for stationary measurements are selected such that the detector element of the sand-detection tool is placed above, across, and below sand-producing intervals for quantifying sand-production rates precisely. Stationary measurements might be repeated for verifying amounts of sand production.
Run in combination with the wireline sand-detection tool, the production logging toolstring was run for determining the multiphase-inflow profile with the following sensors:
- Fullbore and in-line spinners for fluid-velocity measurements
- Electrical probes for water-holdup measurements
- Optical probes for gas-holdup measurements
- Four-arm caliper for measuring inner diameter
- Gradiomanometer tool for downhole density measurements
- Quartz pressure gauge for downhole pressure measurements
- Temperature sensor for downhole temperature measurements
- Gamma ray and casing-collar locator for data correlation
The complete paper presents three field examples, the first two of which are not included in this synopsis in detail. The first example shows application of the sand-detection tool and the production logging toolstring in a well completed with dual tubing at the beginning of its life to produce hydrocarbons from the CH sand reservoir by long string and from the A sand reservoir by short string. The well was later recompleted with single tubing, with sand screens across the A reservoir and a bridge plug set above the CH reservoir.
The second example discusses application of these technologies in a well completed with single tubing, having sand screens set across the A reservoir from the beginning of well life. The main logging objectives for running the sand-detection tool in wells completed with sand screens in the field are to locate sources of sand production and to verify if sand is being produced through eroded intervals in the sand screen, as shown in Fig. 2, or through the entire length of the sand screens because of improper selection of sand-screen type.
Well C. In the third example, Well C was completed with 4.5-in. liner across the CH sand reservoir and perforated across three intervals: 3994–3998 m, 4018–4025 m, and 4032–4036 m. The well was producing hydrocarbons through 3.5-in. tubing with the tubing shoe located at 2509 m. In September of 2018, the well began to produce hydrocarbons with 88% water cut and some traces of sand particles on the surface.
The production logging toolstring with the wireline sand-detection tool was run across the CH reservoir to quantify the multiphase flow profile, identify sources of water production, and locate sand-producing intervals. Data acquired with the wireline sand-detection tool while moving the toolstring showed two sand-producing intervals, one at approximately 4022 m and another one at approximately 4025 m. The energy of sand-grain impacts showed that most of the sand particles have medium and small sizes.
Production logging data analysis showed two producing intervals in this well: 4018–4025 m and 4032–4036 m; the topmost perforated interval was not producing. Most of the fluid (95%) came from the middle perforation, and the remaining fluid was from the bottom perforation. Water was breaking through both producing intervals.
The results of stationary measurements with the wireline sand-detection tool showed that more than 99% of sand was produced from a depth of 4025 m; a remaining negligible amount of sand was produced from 4022 m. Per measured impact energy, half of the produced sand particles were medium in size and half were small.
Based on production logging results and depths of sand-producing intervals, these three perforations were isolated with bridge plugs and the layers containing hydrocarbons located above were perforated. The plug was successfully set at 3973 m. As the result of remedial operation in Well C, the water rate decreased from 520 to 150 B/D and the well stopped producing sand.
In the Lam field, the wireline sand-detection tool was run to determine the root cause of sand production—to confirm if sand was produced through eroded holes in the sand screens, as in the first field example, or through sand screens that are not damaged, as shown in the second field example.
In addition, comparison of multiphase-inflow profiles with sources of sand production showed that most sand was produced through intervals located across the topmost section of the sand screens, marking that part of the sand screens as the point most prone to erosion. Logging results were then used for planning remedial operations to pull tubing out of hole and to replace damaged screens.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 198566, “Locating and Quantifying Downhole Sand Production With Wireline Sand-Detection Tool and Examples of Application in Wells Offshore Caspian Sea,” by Andrey Timonin, Schlumberger, and Eldar Mollaniyazov, Dragon Oil, prepared for the 2019 SPE Gas and Oil Technology Showcase and Conference, Dubai, 21–23 October. The paper has not been peer reviewed.