Sand Production Prediction

Abstract

E&P Exchange Many investigators over the years have researched the causes of sand production and searched for a reliable means to predict it. Sand production prediction is important because of the safety, environmental, and operational concerns involved when produced sand particles fill and plug the wellbore, erode downhole and surface equipment, and increase operating expense. Currently, no method of sand production prediction is universally regarded as accurate and reliable within the industry. A number of prediction models have been developed to identify completions that may be expected to produce sand. Earlier attempts to develop prediction techniques included statistical models, numerical models, mechanical properties logs, sand strength logs, and core studies. Often the individual attempts to develop a predictive model were specific to the type and locale of the reservoir being studied; i.e., water production, pore pressure depletion, perforation geometry, pressure drawdown caused by skin effects, and a variety of other critical parameters were not always considered. The dilemma of an independent U.S. operator faced with a completion decision regarding sand control is not that different from the problems considered by large North Sea production companies. Quite often, the most cost-effective method to determine the need for sand control is by analogy from data collected from offset wells. Complex 3D numerical modeling in concert with extensive laboratory analysis of core and log data is not always economically practical but is the most technically correct method with an acceptable degree of accuracy when properly performed. Historically, much attention has been given to sand production prediction. The vast differences and complexities observed between the models and techniques that have been developed suggests a multitude of engineering and geologic parameters to be considered (Table 1). Morita and Boyd cataloged and analyzed five typical sand problems observed in the field that were induced by (1) unconsolidated formations, (2) water break through in weakly to moderately consolidated formations, (3) reservoir pressure depletion in relatively strong formations, (4) abnormally high lateral tectonic forces in relatively strong formations, and (5) sudden changes in flowrate (cyclic loading) or high flow rate. They developed a core-based completion guide on the premise that completion performance in a weak formation is significantly affected by near-wellbore rock strength and permeability. Morita and Boyd determined that the strength of a reservoir rock varies significantly depending on stress levels and that sandstones deform nonlinearly with the nonlinear character varying with the stress rate. In other words, sandstone failure is a dynamic process that is dependent on changing near-wellbore stresses that are affected by some combination of the 16 factors in Table 1. An evaluation of the completion at one point in time without extrapolation into the future will not accurately predict the conditions under which failure will occur. Sonic, density, and neutron logs relate the well under study to an active sand-producing well. Openhole logs must be calibrated to a known sand producer for an analogous comparison to the well being studied. The problem is that the well must be taken to the point of formation failure before the comparison can be made, and no technique exists for forecasting reservoir performance into the future. Additionally, the effects of pressure depletion, water production(multiphase flow), and additional pressure drops caused by skin effects are not considered. Wells located offshore in the Gulf of Mexico are a good example of this decision criteria. The sand production prediction technique that will be most effective for a given area is one in which field observations, laboratory experiments, and theoretical modeling are all integrated for the formation under study. References Veecken, C.A.M. et al.: "Sand Production Prediction Review:Developing an Integrated Approach," paper SPE 22792 presented at the 1991SPE Annual Technical Conference and Exhibition, Dallas, Oct. 6-9. Morita, N. et al.: "Parametric Study of Sand Production Prediction:Analytical Approach," paper SPE 16990 presented at the 1987 SPE Annual Technical Conference and Exhibition, Dallas, Sept. 27-30. Morita, N. and Boyd, P.A.: "Typical Sand Production Problems-Case Studies and Strategies for Sand Control," paper SPE 22739 presented at the1991 SPE Annual Technical Conference and Exhibition, Dallas, Oct. 6-9. Ghalambor, A. et al.: "Predicting Sand Production in U.S. Gulf CoastWells Producing Free Water," JPT (Dec. 1989) 1336. P. 955^