New Approach on Cement Evaluation for Oil and Gas Reservoirs Using Ultrasonic Images
- Solon Thomasz Coelho de Souza Padilha (Schlumberger Wireline & Testing) | Romero Gomes da Silva Araujo (PETROBRAS, E&P - RNCE)
- Document ID
- Society of Petroleum Engineers
- Latin American and Caribbean Petroleum Engineering Conference, 30 August-3 September, Rio de Janeiro, Brazil
- Publication Date
- Document Type
- Conference Paper
- 1997. Society of Petroleum Engineers
- 5.6.1 Open hole/cased hole log analysis, 1.2.3 Rock properties, 3 Production and Well Operations, 4.2.3 Materials and Corrosion, 1.14 Casing and Cementing, 1.14.4 Cement and Bond Evaluation
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The cement job is one of the final operations during completion and has amajor importance on the performance of the well productivity. A poorinterpretation of the cement job quality due to lack of information can lead towrong decisions, such as inappropriate squeeze jobs and at worse poor reservoirfluid evaluation, usually these operations are expensive and result in highlosses.
The use of high vertical and horizontal resolution quantified acousticimpedance images from ultrasonic measurements brings a new perspective incement evaluation for oil/water wells and combined with traditional CBL-VDL logprovides a complex understanding and definition of cement quality in oil/gasreservoirs helping the completion efficiency. Examples are presented and theinterpretation is discussed showing the superiority of the measurements andresults.
The lack of cement integrity can compromise the final well production andcause unwanted communication between different reservoir zones, which in somecases can result even in ecological damage when, for example, a hydrocarbonzone communicates to an aquifer, situation which can happen where this wascarried on. Cement evaluation logs are being studied more and more in order toachieve a full understanding of the cement quality and performance of thecement job.
The usual interpretation of cement evaluation logs is based on sonic andultrasonic principles, each one has its applications and limitations. Lately,with the introduction of the new wireline logging tool for cement evaluationand corrosion detection by ultrasonics, the USI* (Ultrasonic Imager), thecement quality analysis has had a great improvement due to its high verticaland horizontal resolution of the quantified acoustic impedance image displayand together with the traditional CBL-VDL log, a conclusive interpretation ofthe cement quality can be achieved.
Some problems like gas contaminated cement and channelling have always beencausing doubts on the interpretation of cement evaluation logs and in severalcases increasing costs due to cement correction with squeeze jobs.
The technique proposed here is based on the fact that the information of theCBL-VDL log and the full radial cement acoustic impedance image, provided bythe USI, complement each other, greatly eliminating interpretation doubts andgiving a conclusive definition on the decision to run a squeeze job or not.
The detailed principles of the CBL-VDL (Fig. 1) and the USI (Fig. 2) log iswell covered in the literature and can be found in several technicaldocuments.
The CBL-VDL tool has a monopolar sonic transmitter which works at 20 KHz andthe signal propagates in all directions. The log response, in simple cases, canbe interpreted and provides good information about the cement quality.Nevertheless, due to its characteristics a radial information is not providedand in cases where cement channels occurs, several doubts can arise, resultingin worthless expensive squeeze jobs or at worse the exclusion of a neededsqueeze jobs. Besides, the CBL measurement is affected by microannulus and ingas contaminated cements the CBL-VDL log gives the wrong impression that thecement is good misleading the interpretation. In fact, one should be aware thatthis gas contaminated cement has a reduced compressive strength and due tothat, even if today it is selling the annular space, maybe in the future thecement can break depending on the differential pressures acting on it.
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