Well Testing

Well tests provide invaluable information for establishing reservoir characteristics, predicting reservoir performance, and diagnosing formation damage.

Weatherford has industry recognized world experts in well test analysis. In-house expertise in the associated areas of production log analysis, PVT studies, core analysis, and geomechanics allows a deep understanding of in-well performance. As well as giving expert advice on problematic well tests, Weatherford can also provide routine well test interpretation services.

Well Test Analysis

Well Test Analysis is one of the most important methods available to the reservoir engineer for establishing reservoir characteristics, such as average permeability and compressibility, the position of boundaries and faults.

Well deliverability forecasting can be carried out using flow-after flow testing. The current well deliverability can be found and future production can be forecast.

Under performing production wells are candidates for hydraulic fracturing. However, before any work takes place, a diagnostic well test must be carried out to establish the cause of the low production rate. Potential causes are low reservoir permeability or skin effect due to many factors including wellbore damage, asphaltene deposition, and retrograde condensation (in gas condensate fields). Well test information is invaluable for frac design. After the frac has been carried out, if the well is not performing as anticipated, another well test may be carried out. The nature, and performance of the fractures can be analyzed in PanSystem^® software, and modifications to the frac design can be made for further fracs in the same field.

Figure 1: PanSystem: Analyzing Radial Flow

Vertical (fault planes) and horizontal (shales) barriers often combine to produce a geologically intricate body, which is difficult to analyze using conventional well testing techniques. Weatherford has proven expertise using validated core data to confirm possible interpretations and establish suitable reservoir models and optimum production profiles for complex reservoirs.

Using interference testing, a larger reservoir area can be investigated than is possible using a single well test. Useful information is obtained about the inter-well connectivity, reservoir heterogeneities, and anisotropy.

The determination of permeability and skin allows the precise identification of horizontal well performance based on compartmentalized reservoirs and sweet spots. Weatherford engineers are experienced in horizontal well test interpretation and have presented special seminars on the subject worldwide.

Weatherford has established sound methodology and extensive proven experience in multi-layer well testing.

Good test design is critical in providing data suitable for the chosen analysis objectives. The first step is to choose the appropriate test: build-up, drawdown, multi-layer, interference, etc. For all well tests, suitable rates and times must be chosen to maximize benefits from the test. For more complex tests (multiple-well or multi-layer), test design and methodology are especially important.

Software

Weatherford's well test analysis software PanSystem , the industry leader, has been joined by PanMesh™ and PanScan™ software.

PanMesh software has been designed as companion for PanSystem software, utilizing a newly developed mesh generator and finite element well test simulator.

PanScan software efficiently digitizes paper, foil, or thermal plots, providing a cost-effective solution to the problem of manually transcribing data points into a form suitable for use by PanSystem software and other products.

PanSystem Software

PanSystem software combines in a single program all the functions needed to read in, edit and prepare data as well as perform analysis and simulation. It provides:

• Detailed analysis and simulation
• Production prediction through transient and steady state
• Advanced help with PanWizards
• Complete data editing and preparation

Figure 2: PanSystem Software - PanWizard

PanMesh Software

PanMesh software provides comprehensive mathematical visualization of numerical well test analysis using finite element analysis. PanMesh software is a major step forward in well test analysis and provides:

• Flexible boundary geometries conforming to geological features
• Multi layer capability
• Partial completion options
• Anisotropy modeling
• Pressure transient visualization
• Vertical, deviated or horizontal wells
• Accurate and fast finite element solver technology

Figure 3: PanMesh Software - Finite Element Modeling

PanScan software

Much historical well test data does not exist digitally, and remains unanalyzed and therefore wasted solely for this reason.

To allow the cost-efficient digitization of such data, Weatherford has created PanScan software. PanScan software is a PC-based chart reader for mechanical gauges, printed, scribed, and thermal image plots. It uses input from a high-resolution scanner, allows automatic or manual point selection and digitizes the image efficiently. The input can be scaled using gauge calibration data. The ASCII output files can be read directly into PanSystem software in the corporate preferred unit system.

Figure 4: PanScan Software - Digitizing Plot Data

Well Testing Training

Weatherford has run successful short training courses on well test analysis since 1985. The level of difficulty ranges from beginner to advanced interpretation, with courses on horizontal wells and complex geological environments. Courses take place at Weatherford premises or at client sites throughout the world.

Recent Well Testing Projects

• Analysis of a DST was performed to discover the likely reservoir characterization and to explain an unusual pressure observed during the test. The data was generally of good quality and the reservoir characteristics could be found with a good degree of certainty.
• Over 120 well tests were analyzed and interpreted for permeability determination for the UK and US nuclear industry waste disposal programs.
• Weatherford performed test design, supervision, analysis, and interpretation of a multi-well interference test in a North Sea gas field. This involved 3 wells having simultaneous multi-rate tests, followed by build-ups, and a 4th well used as an observation well. The communication between wells and the gross rock properties could be obtained using PanSystem software. The gas-in-place, Areal heterogeneity, and the level of aquifer support were established.
• A fall-off test in a deviated water injection well was analyzed. A surface pressure gauge has been used. Ranges of permeability and skin were found for each layer. It was concluded that the well tubing was suffering from corrosion. WellFlo^® software was used to model the corrosion and to provide flow correlations to give an indication of the frictional losses in the tubing. The skin predicted in PanSystem software was then modified to account for these losses. The Weatherford engineer's expertise in both well test analysis and well modeling were utilized to give a more accurate picture of the reservoir characteristics.