我最近配置了一台64位Windows 8.1机器，并安装了32位的Visual Studio 2013（至少它安装在Program Files (x86)目录下）。
我还安装了Oracle 11.2.0.1 64位客户端和Oracle Data Provider for .NET。
当我执行gacutil /l | findstr Oracle.DataAccess时，我会得到四个条目，其中包括以下内容：
Oracle.DataAccess, Version=2.112.1.0, ..., processorArchitecture=AMD64
然而，在尝试添加程序集时，我无法在任何列表中找到Oracle.DataAccess（但是在程序集->扩展下存在Oracle.Web）。
我是否需要安装32位的Oracle客户端（或仅32位ODP.NET），因为Visual Studio是32位的？如果是这样，那么软件是否能够在64位系统上运行，使用64位应用程序和64位Oracle客户端（带有64位ODP.NET）？
是的，Visual Studio是一个32位应用程序。
根据您的编译目标（x86或x64或AnyCPU），无论Visual Studio的体系结构如何，运行/调试应用程序所需的Oracle客户端都有所不同。
AnyCPU将在64位Windows上作为64位运行（这很可能���情况）
Oracle.DataAccess没有显示，因为它是一个64位组件库，而您的Visual Studio是32位的。
有几种解决方案：
In Add References use the Browse section and locate Oracle.DataAccess.dll manually. Typically you will find it in folder %ORACLE_HOME%\odp.net\bin\2.x\ or %ORACLE_HOME%\odp.net\bin\4\
Open your *.csproj, resp. *.vbproj file with a text editor and add reference manually, i.e. add lines like this under element <ItemGroup>:
<Reference Include="Oracle.DataAccess">
<SpecificVersion>False</SpecificVersion>
<Private>False</Private>
</Reference>
Note: attributes like Version=... or processorArchitecture=... are not required. Your application will load the correct Oracle.DataAccess.dll depending on selected architecture and target .NET framework (provided that it is installed properly - also on your target machine)
Install both x86 and x64 Oracle Client on your machine. Here is an instruction how to do this: Stack Overflow - Install Oracle x86 and x64
Use the ODP.NET Managed Driver from Oracle. You can download it from here: 64-bit Oracle Data Access Components (ODAC) Downloads This works also with 32bit applications.
Open your Registry editor and check if RegKey HKLM\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727\AssemblyFoldersEx\ODP.NET resp. HKLM\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319\AssemblyFoldersEx\ODP.NET exist. Both RegKeys contain only the (Default) value with location of your Oracle.DataAccess.dll.
Example:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727\AssemblyFoldersEx\ODP.Net]
@="c:\\oracle\\product\\11.2\\Client_x86\\odp.net\\bin\\2.x"
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319\AssemblyFoldersEx\ODP.Net]
@="c:\\oracle\\product\\11.2\\Client_x86\\odp.net\\bin\\4"
Check your target Framework in compile options. When you have ODP.NET version 4.x installed you must select target .NET Framework 4 or higher in order to see the ODP.NET entry in reference list.