This paper_ pI8IllIIIld for pr8S«1lation at1he 1994 PelItlIeum ConIeI1ll1C8 and Exhibition of Mexico held in Veracruz, MEXICO, 1()'13 OclDber 1994. This JllIIl8r _ selected for plllSllnlalion by an SPE P~ram Committee lolowing lllYiew of information oontained in an absllllct submillad by 1he aulhor(s). Contents 011he paper, as preS«lted, haw not been nMewed by 1he Society of Petroleum Engineers and are subjeclto OOll8Ction by the aulho'1s). The ma18riaJ, as presented, does not necessanly reftecl an~position 01 1he Society 01 PlIlrdeum Enslir-rs, its OIlicers, or members. Papers pr8ssnted at SPE meetings are subject to publcalion IIIYiew by Edi1DriaJ Commillees of1he Society of Pelroleum Engineers. Pennission to copy is restriCted to an abstract of not more than 300 words. lUustrations may not be~ed. The absll8cl should contain oonspicuous acknowledgrrient 01 where and by whom 1he paper is p-m-d. Write Ubnuien, SPE, P.O. Box 833836, Richardson. TX75Oll3--3838, U.S.A. Telex, 163245 SPEUT. Harmonic: (b=l) BRIEF SUMMARY This paper presents rigorous methods to analyze and interpret production rate and pressure data from oil wells using type curves to perform decline curve analysis. These methods are shown to yield excellent results for both the variable rate and variable bottomhole pressure cases, without regard to the structure of the reservoir (shape and size), or the reservoir drive mechanisms. Results of these analyses include the following:• Reservoir properties: -Skin factor for near well damage or stimulation, S -Formation permeability, k • In-place fluid volumes:-Original oil-in-place, N -Movable oil at current conditions, N p • mov -Reservoir drainage area, A We have thoroughly verified these analyses and interpretation methods using both synthetic data and numerous field examples. In addition, we provide illustrative examples to demonstrate the ease of analysis and interpretation, as well as to orient the reader as to what are the benefits of rigorous decline curve analysis. INTRODUCTIONThe importance of performing accurate analysis and interpretation of reservoir behavior using only rate and pressure data as a function of time simply can not be overemphasized. In most cases, these will be the only data available in any significant quantity, especially for older wells and marginally economic wells where both the quantity and quality of~types of data are limited. The theoretical application of this technique is for newer wells, at pressures above the bubble point, although we show that the methods described here can be accurately applied at any time during the depletion history of a particular well. The development of modem decline curve analysis began in 1944 when Arpsl published a comprehensive review of previous efforts for the graphical analysis of production decline behavior. In that work, Arps developed a family of functional relations based on the hyperbolic decline model for the analysis of flow rate data.References and illustrations at end of paper Arps' efforts provided a variety of results...

In this article we generalize the concept of the pseudosteady-state productivity index for the case of multiple wells producing from or injecting into a closed rectangular reservoir of constant thickness. The work complements the analytical study by Rodríguez and Cinco-Ley 1 for systems produced at constant flowing pressures. Wells are represented by fully penetrating vertical line sources located arbitrarily in a homogeneous and isotropic reservoir. The multiwell productivity index ͑MPI͒ is a square matrix of dimension n, where n is the number of wells. The MPI provides a simple, reasonably accurate and fast analytical tool to evaluate well performance without dividing the cluster into single-well drainage areas. The MPI approach is used to obtain approximate analytical solutions for constant ͑but possibly different͒ wellbore flowing pressures, and to visualize the resulting pressure field. In addition, the skin factor trace technique is introduced as a tool to monitor a cluster of wells. The MPI technique is illustrated using a synthetic example taken from Ref. 2, as well as two field cases.

Thii paper was sefeded Ior preeenfefiin b an SPE Program CernmMee foflowing review of hfom'don cmfained in an ebalmct submilted by the author(s). contents of the paper, es pmaanfed, J have nof been re-by the Society of atroieum Engineers and are s@ed 10 mredion by the atifsotts). Tfm malarial, es presented, does nof nemaeeri Pefroleum Engineers, ile officers, or memlxrs. Papets presented at SPE maelinge are sbjecf to fymffadwvfdIbfrOf ti~of *stmdshldatain@ns@WWa-@gmeti ofnhereandbywfmmt hepeperia fion rakiaw by Edttil Carmlltees of fm Society of Pafrdeun Enghears. Penniaekm 10 COPY is restkl~10 an abstract of not more t~n 300 WOI@S. llluslra~ons may not be @.

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This paper presents both downhole and surface tiltmeter hydraulic fracture mapping results of five fracture treatments (in two wells) in the Clearfork formation located in the North Robertson Field, West Texas. This field is under waterflood and both injectors and producers are generally fracture treated in three stages at depths of roughly 6,000 to 7,100 feet.Surface tiltmeter mapping was performed on all five treatments to determine hydraulic fracture azimuth and dip. Downhole tiltmeter mapping was performed on 2 treatments in one well to determine the fracture geometry (height and length). In addition, other diagnostic technologies such as fracture modeling and radioactive tracers were used and their results and conclusions are discussed in conjunction with tiltmeter mapping. Understanding hydraulic fracture growth is of critical importance for evaluating well placement and the risk of communication between producers and injectors and to assess fracture staging, perforating and well performance issues. Introduction The North Robertson field is under waterflood and both injectors and producers are generally fracture treated in three stages. The target zones were the oil-producing Lower, Middle and Upper Clear Fork carbonate formations at depths of roughly 6,000 ft to 7,100 ft. Knowing the azimuth, dip and geometry of hydraulic fractures is critical for evaluating well placement strategies for waterflood applications. Surface and downhole tiltmeter fracture mapping are technologies that provide these important measurements of fracture azimuth, dip and geometry. Tiltmeter fracture mapping has previously shown that fracture azimuth and dip can change dramatically in waterflood areas due to local variations in reservoir pressure. This can result in hydraulic fracture reorientation that can cause waterfloods to "short circuit", thereby significantly reducing sweep efficiency.